A reservoir stratifies in winter with the coldest, densest water at the bottom, and most dams release from near the bottom, so the river below comes out at nearly the same temperature in January as it did in October: cold, but well above freezing, and remarkably stable from day to day. That stability is the whole reason tailwaters are where the West fishes in winter. The fish never get the shock of an overnight freeze, the insects never get scoured by anchor ice, and the flow is set by an operator rather than by the weather.
Why a dam release keeps a river open
Three things follow from a bottom release. First, the water does not freeze for several miles below the dam, so there is no shelf ice and no slush to foul a drift. Second, because the temperature barely moves, the trout's metabolism barely moves either; a tailwater fish in January is slower than in June, but it is feeding every day. Third, the steady flow and temperature grow a dense population of small food: midges, Baetis, and on the richest rivers scuds and sowbugs, crustaceans that are available every month of the year.
The cost is that a tailwater's flow can change on a schedule that has nothing to do with fishing. Winter releases are often low and stable, but a power-demand or reservoir-management change can bump the flow overnight. Every river page on this site carries its USGS gauge; check it the morning you go.
The tailwaters on this site and their winter hatch rows
Twenty-five rivers here carry a tailwater water type. Their January rows fall into three groups.
Blue-Winged Olives peaking in January
These are the rivers where the Baetis row is marked peak in January, not just on. Midges are also at peak on every one of them.
- Bighorn River, Montana and the Missouri River, Montana: BWO and midge at peak, and a sowbug/scud row marked peak all twelve months.
- Frying Pan River, Blue River, and Taylor River in Colorado: BWO and midge at peak through winter; the Frying Pan is also the only river here with a Red Quill row, though it goes quiet until March.
- Truckee River, California, Truckee River, Nevada, and the East Walker River: brown-trout tailwaters with BWO at peak all winter.
- American River and Upper Sacramento in California, and the Salt River near Phoenix: low-elevation water where winter is arguably the best season of the year.
- Colorado River at Lees Ferry: midges at peak every month of the year and BWO at peak through the winter.
The San Juan River below Navajo Dam is listed with the water type Below Navajo Dam rather than Tailwater, but it belongs in this group: its midge row is marked peak in all twelve months and BWO is at peak from October through April.
Midges peaking, Blue-Winged Olives on
On these the winter BWO is present but thinner; midges carry the day.
- Utah: Provo River, Middle Provo, Weber River, Ogden River, Strawberry River. On the Provo and Weber the BWO row is at peak by February.
- Colorado: Colorado River and Gunnison River, both with BWO reaching peak in February.
- Wyoming: North Platte, Green River, Shoshone River.
- Idaho: Big Wood River and the Boise River.
The Green River below Flaming Gorge
The Green River, Utah is the outlier. Its BWO row is off in January and comes on in February, but its scud row is on every month and its midge row is at peak through the winter. It is a scud-and-midge river until the Baetis start in late winter.
Fishing the release schedule
Because the water is clear and the fish are slow, flow changes matter more on a tailwater in winter than at any other time. A rising release pushes fish out of the middle and onto the edges and can put them off for a day. A falling release concentrates them and often turns them on. The ideal is several days of the same number on the gauge.
Know who operates the dam and whether releases follow a daily pattern. When the flow is up, fish the soft edges and the tailouts. When it is low and flat, the fish are in the deepest, slowest water and you need to get the flies down to them without spooking the pod.
Rigging for winter tailwater fish
- Nymphs. A two-fly rig under a small indicator: a sowbug or scud pattern (Ray Charles or a pink or olive scud, size 16 to 18) on the Bighorn, Missouri, and Green, with a Zebra Midge size 20 to 24 below it. On the Colorado and Utah tailwaters, a Baetis nymph or RS2 size 18 to 22 with a midge below. Enough split shot to tick bottom, and adjust it every time you change depth.
- Tippet. 6X fluorocarbon for the nymphs, 6X or 7X for dries. The water is low and gin-clear and the fish have seen every rig there is.
- Dries. When BWOs come off on a gray afternoon, a size 20 to 22 Parachute Adams or a CDC Baetis emerger. When fish are dimpling on midges, a Griffith's Gnat or a size 22 midge adult. Fish them on long leaders, downstream, with a reach cast.
- Streamers. On brown-trout tailwaters like the Truckee, East Walker, Weber, and Taylor, a small sculpin pattern swung slowly through the deep water on a warm afternoon can move a big fish that ignores nymphs. Slow is the operative word.
Crowds and etiquette below the dam
Open water concentrates people the same way it concentrates fish. The first mile below a dam on a January Saturday can be shoulder to shoulder. Walk downstream; the fish are stacked in the same slow pools a mile down with no one on them. Give an angler working a pod the whole pool, and if you are the one on the pod, rotate out after a few fish.
Before you drive to a tailwater in January
- Pull up the USGS gauge on the river's page and look at the last week, not just the current number. Flat is good.
- Check the dam operator's release schedule if one is published.
- Check the state fish and wildlife agency for the current regulations on that stretch. Several of these rivers have special regulations and they change.
- Bring midges in three sizes, one scud or sowbug pattern, and a spool of 6X. Leave most of the rest at home.