Summer Streamflow and Fishing Forecast, Mid-May Update, by Walter

Summer Streamflow & Fishing Forecast, Early May Update


We had an exceptionally wet and fairly cold winter that saw snowpack peak at upwards of 175% of normal for the date in the Upper Yellowstone River Basins in Yellowstone Park and Montana, the most important basins in our operations area, and between 125% and 150% of normal in other basins. This resulted in the deepest snowpack as of mid-April since 2011 and the second-deepest since 2008. Since mid-April report, we’ve experienced generally warm and dry conditions punctuated by a brief burst of cold/wet at the end of April. The snowpack therefore began to crumble at least a week early, and is melting quickly. The spring runoff is aggressive and heavy. In fact, points further west in Montana where it is warmer are seeing flooding because of the speed of the melt. This early warmup is going to play a huge role in getting runoff through and done with. Whereas we thought in mid-April that area waters would drop out of runoff as much as three weeks later than their median date for doing so, we now believe this will take place no more than a week or so late. Snowpack now ranges from 111% of normal up to 139% of normal for the date in our operations area, a huge drop from early April and approximately in line with where we were in 2014 and only a little higher than we were last year at this point.

Want the short and sweet version? We’ve transitioned from expecting a drastically late end to runoff to a date within the “normal” range, albeit towards the latter end of it. For much the same reason, we now expect near-normal summer fishing conditions, with the major exceptions that there will be A LOT of standing water around in June and July (hooray mosquitoes) and flows will remain somewhat higher than normal through the summer, though not so high as to drastically change fishing techniques/tactics/hatches after about July 15.

Read on for more details on what we expect/predict for various waters, both in terms of dates given waters will drop out of runoff and how they will fish through the core June-October season.

Note: Make sure to check this page as well as the general fishing report link in the menu next Thursday, May 24, or Friday, May 25. The Yellowstone Park fishing season opens the 26th and we will be putting out full and in-depth reports just beforehand.

Why Does Snowpack and Runoff Matter?

This is for readers unfamiliar with the western water year and how it impacts fisheries. Old hands can skip this bit.

Simply put, mountain snow that falls from sometime in October through April as well as how and when this snow melts off between April and June are the primary drivers of late spring and early summer (May to early July) water clarity, stream flows from May through early fall, and therefore fishing on all bodies of flowing water that are not dam-controlled (freestone streams and rivers instead of tailwaters), and they play a large role (particularly in water level and applicable fishing techniques) even on waters that are controlled by dams. The amount of winter snowpack even plays a large roll in summer and early fall water temperatures, even though the snow has long-since melted. Summer rains usually only cause brief blips in flows, with the overall chart of flows through this period dominated by snowpack and runoff. Only in the fall does rain play a large roll.

The water year works like this: Every body of water drops to low/cold winter flows sometime in October or early November at the latest and stays at this same approximate level until sometime in spring, usually March. At this point flows begin creeping upward due to low elevation snowmelt, though clarity and water temperature are seldom impacted until sometime in April. Freestone waters usually rise slowly. Dam-controlled waters may spike much earlier, typcially rising in a series of steps, as water managers make room in the reservoirs for the upcoming heavy melt. In April, brief warm spells bring down short shots of muddy water that dirty and raise freestone streams substantially but temporarily, after which the river drops and clears and continues the slow, steady rise of March. Tailwaters usually consider their slow rise save following exceptionally dry winters. Sometime in late April or early May, the first true warm weather hits, bringing 70+ degree temps to the valleys and above-freezing nights up to the highest mountains. This is when the real runoff begins. For a month to two months depending on snowpack, the date runoff begins, and how hot it gets in May, freestone waters will be filthy muddy and raging high.

Every freestone (non dam-controlled) body of water now spikes sharply with the hit of snowmelt, rising as much as several FEET per day for the larger rivers, with yo-yoing flows depending on the day/night temperature swings, any brief cold snaps that slow the melt, and if warm rain falls on snow, which accelerates the melt. Looking at a streamflow graph, flows rise in an upward-trending sine wave. On small drainages, the rise period usually lasts only a couple weeks. On large rivers like the Yellowstone, the rise might last a month or more.

Peak runoff here typically occurs in the last week of May or first week of June, with some drainages draining high mountains sometimes seeing flows peak in mid-June, particularly in years with high snowpack and late starts to the melt. The precise level varies hugely by year. The more winter snow and the faster it melts, the higher the peak. On the Yellowstone River, the peak is usually from 15,000 cubic feet per second (following dry winters) to 28,000cfs (in wet/cold winters), but can crack 30,000cfs following exceptionally cold winters with abrupt beginnings to the runoff. Winter flows on this same stretch of river are 750-1000cfs. What’s this mean in practical terms? It means that a low, rocky, structured body of water becomes a raging chocolate fire hydrant flowing well up the banks, with full-sized trees torn from the banks, dead animals that tried to swim across, and potentially even human structures floating downstream at 10mph. To those unfamiliar with the spring melt, peak runoff will look like “flooding” even in a normal year, since the river will ALWAYS inundate bankside trees and bushes and will always be filthy brown and full of detritus. There can also be full-scale flooding, particularly in exceptionally high-snowpack years. This is why buying/building a riverside house on the Yellowstone is a terrible idea… Suffice it to say, there’s no fishing at anywhere near peak runoff. In fact, even the beginning of the melt sees water that’s too muddy to fish, even if it’s not too high.

From the peak of runoff through at least early September and usually early October, water levels on freestone rivers and streams gradually but steadily recede. Because the rising water a month or two earlier scours all dirt, sand, mud, loose grass, pine needles, and other junk off the rocks, freestone streams clear at a much higher level than they get dirty. While the Yellowstone might get too muddy to fish as it rises over about 2500cfs, it can clear enough to be fishable at 12,500cfs (in wet years), though 9,000-10,000cfs is more typical. The streams will still be racing up in the willow bushes when they clear, however, so fishing quality just after runoff recedes a bit depends on quality strucutre like large bankside boulders, eddies, etc. Almost all structure will be near the bank at this time. Waters that lack large structure, such as meadow streams with a bottom composed of gravel (i.e. Slough Creek), need to drop more than the larger, rockier waters to become fishable. Once peak runoff is past, tailwaters are typically drawn down much more quickly than freestone rivers, then kept at this moderate level through the fall.

After runoff recedes for a given body of water to become fishable, the snowpack still dictates much of how it will fish through the season. Generally speaking, once runoff is past, higher streamflows through the summer lead to better fishing. Higher water is generally colder water (on average), which reduces the potential for high water temperature problems in August, it is always faster than lower water and therefore pushes the trout towards the banks where currents are slower and the trout are easier to catch, and it makes delicate presentations and tippets less necessary. Late summer streamflows almost always track with the overall snowpack level and when it started melting. In low-water years like 2015, the Yellowstone may drop out of runoff June 15, drop below 4000cfs on July 10, and drop below 1500cfs by late August. This is low for the core season. In high but not extraordinary water years like 2014, the river drops out of runoff around July 5-10, drops below 4000cfs around August 10, and remains above 2000cfs through September.

Until flows drop dramatically in late August or September, rain storms have little effect in changing the above picture. The slow drop in flows may pause or reverse itself for a few days, and on rivers with mud banks like the Lamar, Gardner, and points downstream on the Yellowstone rain may cause streams to get muddy for a day or two, but once this “blip” flushes through, the drop will continue as though nothing happened. Only in the fall can rain events dramatically raise flows and keep them elevated for a week or more. This is most common after the middle of September and does not impact tailwaters.

In sum: high snowpack and/or a late start to the melt = high and prolonged runoff and a later start to the season on a given body of water, plus higher water through the season, with generally easier/better fishing. Low snowpack especially when coupled with an early start to the melt = a brief and low runoff and an earlier start to the season (and therefore better fishing in June and early July, but low and warm water in late summer and therefore tougher fishing from late July through early September.

Water-Specific Predictions

Yellowstone River Drainage Inside Yellowstone Park

Note: The Lamar River and Gardner River Drainages are discussed in their own entries below.

Yellowstone River Above Yellowstone Lake: This water opens July 15 and will still be very high, but fishable. This fishery is not what it was before the mid-90s, but if you are making the trip there should still be good numbers of post-spawn cutthroat that have not yet returned to Yellowstone Lake through mid-August.

Yellowstone River, Lake to Falls: Same as above, but a much better option since 30+ mile hikes are not required. You might be fishing around the picnic tables around Nez Perce Ford on July 15, but the water will be clear.

Yellowstone River, Grand Canyon (Falls to Lamar): Will be cement-colored and massive on the opener and will not be even marginally fishable before July 1. The most likely bet right now is that this water will fall into shape between July 4 and 10, with stonefly nymphs and streamers out of the gate followed by the Salmonfly hatch by July 15. The Salmonflies MIGHT last until August 1, certainly til July 25. Good (high) flows should lead to excellent fishing through September at least.

Yellowstone River, Black Canyon (Lamar to Gardiner): Will not be fishable prior to July 4, with best fishing after July 10. Salmonflies about the same time and lasting through at least the 25th and probably August 1 near cold tributaries in the upper canyon. Good fishing will continue through September, but it will be REALLY physically prior to about August 5, since the river will still be in the bushes until then.

Yellowstone River Tributary Creeks in YNP: Blacktail and Cascade should become fishable in the last week of June. Others won’t be worth it until July 20 or so and will be best in August and early September.

Yellowstone Lake: Will be massively high but fishable on the opener on May 26. The best fishing as always will occur prior to August 1.

Other Lakes and Ponds in the Yellowstone Drainage in YNP: All will likely be ice-free on the opener, but impossible to reach until June 10 or so due to swamp and snow drifts on the trails. The best fishing will be in June and early July except on Blacktail, which is closed until early July to protect nesting birds.

Yellowstone River Drainage Downstream of Yellowstone Park

This stretch of river will be a huge beneficiary of the early start to the runoff. We anticipate it will become fishable as much as two weeks earlier than previous estimates (though still not “early”).

Yellowstone River, Gardiner to Carbella (Upper Yellowstone and Yankee Jim Canyon):Will come into play sometime in the first ten days of July. The precise date will depend on how warm and wet the period from May 15 through June 15 turns out to be. In a change from previous posts, we now expect a fishable and possibly very good Salmonfly hatch on this water, almost certainly for the week or so immediately after it gets clear enough to fish (likely at about 11,000cfs flow, which means a boat will be necessary). Water levels should remain excellent through the summer. Yankee Jim Canyon will become floatable sometime in the first half of August and remain floatable for five weeks, and possibly through September if late summer and early fall see reasonable amounts of rain. We expect very good attractor and terrestrial dry fly fishing here beginning no later than July 20 and continuing through September.

Yellowstone River, Carbella to Carter’s Bridge (Paradise Valley): Will become fishable in the first 10 days of July but likely won’t be quite as good as the “upper” before July 20-25, since this stretch has less obvious structure to concentrate the fish. That said, the Salmonflies will PROBABLY be fishable for 4-5 days right after it clears from Carbella to Loch Leven. The best big-fish fishing will occur subsurface here from July 20 through mid-August, with some reasonable big hopper-eaters from August 10 through mid-September or so. Smaller attractor/caddis fishing might be so-so this year until early August due to the high water. The big fish don’t like to rise on this stretch til the water drops a bit. The fishing should remain good throughout the season here.

Yellowstone River, Carter’s Bridge to Laurel (Lower Yellowstone): Will fall into shape about 10 days after the rest of the Yellowstone north of the park and won’t see any Salmonflies, but will otherwise fish similarly to the Paradise Valley stretch.

Yellowstone River Tributary Creeks Outside YNP: Don’t even think about it until August 1. The latter half of August will be best on all, except perhaps RIGHT at their confluence with the big river, where they will fish at the beginning of the season too.

Paradise Valley Spring Creeks: These are not impacted by runoff and as always are best February-April, late June through July, and early October through November.

Private Ranch Lakes Feeding the Yellowstone: Not impacted by runoff, though snowdrifts made Story Lake hard to reach before April 20 and so they got a bit of a late start. Story will fish well through sometime in late June, Burns through sometime in mid-late July, with the precise dates depending on early summer warmth.

Lamar River Drainage

Lamar River Mainstem: Will become fishable sometime between July 5 and July 20, probably sometime between the 10th and 15th (my money is on the 15th in the meadows and the 10th in the canyon). There will be plenty of water to offer good hatches and dumb trout through September. Wading may be sketchy before mid-August because the bottom gravel will be pushed around a lot by this runoff.

Soda Butte Creek: Generally similar to the Lamar. Expect major changes to the streambed due to the runoff this year. We expect the Soda Butte-Lamar confluence to be a vast lake on June 1 this year, and the channel both streams choose to take after the water recedes is anybody’s guess.

Slough Creek:Fishable between July 5 and 15th, probably around the 10th, with the Lower Meadow fishing better than the upper meadows for the first week to ten days. The best fishing will occur prior to August 15, with another uptick perhaps in mid-September. The Green Drake complex of insects should hatch well after July 20.

Other Streams: The upper Lamar tribs will be worth checking out as soon as the Lamar drops into shape. They should be very good in late July and early August. The Buffalo Fork of Slough MIGHT see a rainbow eradication project begin this season. Keep track of our fishing report for details if/when this happens.

Trout and McBride Lakes: Trout Lake will be fishable but hard (as always) on the opener and will fish best before early July. McBride will probably be impossible to reach unless you want to swim across Slough Creek prior to August 1.

Gardner River Drainage

Gardner River and Tributary Creeks Upstream of Osprey Falls: Will begin falling into shape after July 1, with Winter/Straight/Obsidian Creek the first to become fishable and the Gardner mainstem the last. The Gardner probably won’t be ready until July 15 up here. All streams (which universally hold beginner-friendly brook trout averaging 5-8 inches, with a few rainbows in the Gardner running a bit bigger) will fish best in late July and early August, and taper off by Labor Day.

Gardner River, Osprey Falls to Yellowstone River: May be fishable on the opener or anytime in June particularly below Boiling River IF AND ONLY IF we have a prolonged cold snap to pause the runoff. About 2 days of subfreezing nights without moisture at high elevation are required for there to be a shot, with the longer the cold spell, the better the shot. You need 18 inches of visibility. Even if you have the visibility, expect hyper-challenging wading and crashing through bankside brush to be required to catch fish. That said, if the water is clear enough and you can handle the wading, the fishing is very good with large stonefly nymphs. More realistic fishing will begin sometime in the first ten days of July when the runoff recedes for good. Stoneflies will hatch soon after below Boiling River and after July 15 above Boiling River. We expect a few Salmonflies to be present in Sheepeater Canyon through the first week of August. Standard attractor/hopper/dropper fishing will be good all summer, including below Boiling River, since flows should be high enough and cold enough to keep the algae down pretty well.

Other Streams: Will become fishable after July 4, best after July 15, and remain fishable until mid-September.

Small Lakes: These will as-always be best in June and perhaps the first week of July. The problem is going to be access. Some combination of sucking thigh-deep marsh, hard stream crossings, and snow across the trails will be obstacles in reaching all except Joffee Lake. Trails to Grizzly Lake remain tough to access due to the ongoing Norris-Mammoth road construction.

Madison River Drainage Inside YNP

Firehole River: This will probably be the only flowing water option in Yellowstone Park on opening day (May 26), which isn’t unusual. Even so, it will probably still be high (up in the grass), cold, and the color of tea with cream. Streamers will likely be the best bet. Peak runoff will likely occur on or near the opener. Hatches will be fragmentary at best before the first week of June. The best fishing before June 5 will be from Midway Geyser Basin (the Muleshoe) up to Biscuit Basin, where the percentage of warm/clear geyser water is highest. After June 5, the fishing–particularly dry fly fishing–will improve. The best fishing will be from June 5 through June 20. Fishing should remain good especially in the mornings except on hot/bright days through June, and perhaps extend into July. As usual, only the water upstream from the Old Faithful closure area will fish well from early July (or late June if it’s hot/dry) through Labor Day. After Labor Day, the fishing will steadily improve into October and remain good through the close of the park season on the first Sunday in November.

Gibbon River:Will become fishable in the rugged and structured canyon section between June 1 and June 10. Earlier if the current warm pattern continues, later if it cools off again in May. The best fishing will occur from June 10 through early July. Elk Park and Gibbon Meadow will fish best between June 20 and July 10. The upper river from Grebe Lake to Virginia Cascades is closed this year for a westslope cutthroat and fluvial (river-dwelling) grayling reintroduction project. Norris Meadow is never good due to the campground, but if you insist on fishing it, go after June 20 or so.

Madison River Above Riverside Drive: This stretch of the Madison will likely be too high for the first week of the park season. It should fall into good shape June 1-5, with the best early season fishing from June 10 through 25. After that, mornings should be good until mid-July. We now anticipate too-warm water in late July and August, with fishing improving through September and great in October.

Madison River Below Riverside Drive: As always, this is fall-only water and is the most famous fall-run brown and rainbow water in the region. Don’t bother before Labor Day unless you know your business, in which case August 20 is reasonable if it’s cool out.

Grebe and Wolf Lakes: Closed this year due to the grayling and westslope cutthroat reintroduction mentioned above.

Other Waters: Firehole tributaries will be best in July and August, as usual. Solfatara Creek (Gibbon trib) will be best in July and August, but has some opportunities September-October too.

Madison River Drainage Outside YNP

Between the Lakes: Fishing now above Cabin Creek, muddy below. Crowded and likely to stay that way until runoff recedes elsewhere.

Quake Lake to Ennis Lake: Will be too high albeit not necessarily muddy (particularly upstream of the West Fork) until probably June 20-25. Will still be raging and very physical to fish after that, until mid-July. Salmonflies will probably start around June 25.

Ennis Lake to Three Forks: Will be very high but probably clear enough except for a couple weeks in late May, particularly upstream of Cherry Creek. Will see heavy guide pressure as this will likely be the only drift-fishable water between Livingston and Helena until the upper Madison clears in late June. Crayfish will be the top bet, as always.

Hebgen and Quake Lakes: In the process of losing their ice. Will fish fine all summer, as they are not impacted by runoff, with the exception of the short runoff cycle of the creeks feeding the “between the lakes” stretch making the upper end of Quake muddy in May.

Missouri River Mainstem

Three Forks to Canyon Ferry: This is basically carp water with a few trout near cold tributaries and in the fall when they run up from Canyon Ferry Reservoir to Toston Dam. The best fishing is always in August and early September for carp and in October and November for Trout, and that isn’t going to change this year.

Hauser Dam to Holter Lake (“Land of the Giants”): Will be very high but fishable all year. The high water means fishing from a boat is the only reasonable option until mid-late June. Think 14-foot leaders, #12 sowbugs, and three or four BB split shot. This is probably my (Walter’s) personal favorite option from May-early July under current conditions. It requires a jet boat equipped with oars to fish successfully, which I just so happen to have… (discounted rates this season due to the lack of other options). The average fish here average over 18 inches and they should be fat and feisty this year.

Holter Tailwater (the Famous Bit): Like the Hauser Tailwater, will be raging high. Might reach 16,000cfs in late May, which means fishing 16-foot leaders and #4 Wire Worms in the campgrounds, literally. That said, the fishing will be good provided your nymphs (only nymphs) are on the bottom. Flows will drop to something resembling normal (around 4,000cfs) in late June or early July, after which good PMD, caddis, Trico fishing should commence.

Other Yellowstone Park and Montana Waters (Generally Outside the PFS Operations Area

Gallatin River: Like the Yellowstone, will be very high until early July. After that, will fish well on attractor, terrestrial, and stonefly dry/dropper combos into fall.

Lewis and Snake Rivers in YNP: While the Lewis (as well as its headwaters lakes) may be clear and ice-free by mid-June, they will be so high that I wouldn’t bother. Check back mid-October for the brown trout run. The upper Snake in YNP will be too high until at least mid-July.

Bechler River: Mosquito-infested swamp until early August even in average years. This year I wouldn’t bother until late August.

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