A river the headgates run
The Jefferson starts where the Beaverhead and Big Hole meet at Twin Bridges and runs 77 miles, by FWP's count, to Three Forks. FWP's own summary is blunt: it is used heavily for irrigation and is subject to severe dewatering in low-water years, and the Ruby and Clark Canyon reservoirs upstream shape its flow. Before the current drought plan the USGS recorded flows below 5 cfs in 1988. That history is why every angler here should know two numbers from the Twin Bridges gauge on this page.
Under the Jefferson River Watershed Council's drought management plan, 600 cfs at Twin Bridges is the awareness threshold, when voluntary conservation starts and a press release goes out. At 280 cfs FWP may evaluate a fishing closure, and any closure stays until flows exceed 300 cfs for seven straight days. The plan's goal in the worst of it is to keep at least 50 cfs at the Parsons Bridge gauge near Waterloo. Temperature triggers run alongside: at a 68 degree daily maximum anglers are asked to fish mornings, and three straight days at 73 lets FWP impose hoot-owl hours, 2 p.m. to midnight. In 2026 that happened on July 15 for the entire river, and it was lifted August 31. Twin Bridges touched 277 cfs on August 12 and Parsons Bridge bottomed at 73.5 the next day.
Hell's Canyon to Cardwell: the valley floats
FWP river miles are measured up from the mouth, which makes planning floats simple arithmetic. Hell's Canyon FAS (mile 70.7, gravel ramp) is the first site below Twin Bridges, and Silver Star FAS (mile 66.0, concrete ramp) is five miles on; Clark camped near Silver Star on August 4, 1805. Below Silver Star the river braids through open valley for about 16 miles to Parrot Castle (mile 50.3, no boat facilities). Watch for the Parsons diversion dam at the Waterloo Bridge, a pile of boulders across the river that the Jefferson River Canoe Trail says can cause a bad accident; it was rebuilt in 2014 with a pass-through chute, and the portage is on the left. Parrot Castle has its own diversion dam. Kountz Bridge FAS (mile 44.2, concrete ramp, 6 miles southwest of Whitehall on Kountz Road), Mayflower Bridge (40.5) and Cardwell Bridge (35.5) split the middle river into short floats of four to five miles.
Montana Angler describes this whole reach as big open valley where large territorial browns hold in the undercut banks, with trout numbers lower than on other rivers nearby, and rainbows returning to the upper river after landowner and Trout Unlimited work. Fish the bank on the outside of every bend and do not expect a lot of fish.
The canyon, Sappington and the last miles to Drouillard
Below Cardwell the Boulder River comes in and the Jefferson tightens into a single channel through the seven-mile Jefferson Canyon. Limespur FAS (mile 29.5) is walk-in, Sappington Bridge (21.7) and Williams' Bridge (18.5) have gravel ramps, and the canoe trail calls Sappington to Williams the most used stretch on the river. A diversion near Sappington is now as big as the one at Parsons Bridge. Drouillard FAS (mile 7.6) is the last ramp before the confluence, and most floaters take out at Missouri Headwaters, just below where the Gallatin comes in. Camping is limited to a few BLM parcels such as Point of Rocks and Canyon Corner, a state parcel at the Willow Creek mouth, Shoshone Landing, and below the high-water mark. Lewis named Willow Creek the Philosophy River on July 30, 1805, two days after he and Clark named this fork for the President.
One rainbow, no limit on pike
The 2026 FWP regulations list the whole Jefferson in the Central District, open all year. The river's own rule changes the trout limit: 3 combined trout daily, only 1 over 18 inches and only 1 may be a rainbow. Northern pike have no limit. Arctic grayling, which FWP lists as native here, must be released immediately. At the mouths of Hells Canyon Creek and Willow Springs Creek, fishing is closed 100 yards upstream and downstream from April 1 to 30 and from September 30 to November 30. The Jefferson is listed as Eurasian watermilfoil water, so collecting bait animals is not allowed. There are no tackle restrictions. FWP shows no stocking records for the river.
Reading the Twin Bridges number
No shop publishes a wading or floating band for this gauge, so the 700 to 1,200 cfs range on this page is the USGS record for the post-runoff fishing season: the long-term August mean at Twin Bridges is 702 cfs, September 849 and October 1,203. June averages 4,948, and Montana Angler says the river usually becomes fishable after snowmelt between June 10 and 15. Below 600 you are in drought-plan territory, and below 280 check FWP before you go. In fall, Montana Angler warns that a sudden rise of more than 150 cfs when farmers shut their ditches can put fish down for two days or more; in September 2026 Twin Bridges climbed from 469 to 1,020 cfs in three days. By early December, slush usually ends the season.
Stoneflies, PMDs and a bank full of hoppers
Montana Angler's Jefferson chart starts with Skwalas in mid to late March, size 8 or 10 and sporadic, and blue-winged olives from late March through May, best on overcast days around Silver Star and the Highway 287 bridge. Western March Browns need 44 to 48 degree water. Mother's Day caddis come off before runoff if the water reaches the mid 50s, and caddis are thick again right after runoff and into July. Salmonflies in the first two weeks of June are sporadic at best; golden stones follow from mid-June into early July, and Yellow Sallies, mostly 10 and 12, from mid-June into July. PMDs, size 16, peak in late June and early July and fade once the water is over 65. From late July hoppers, ants and beetles carry the fishing along the grassy banks, and trout stay active if the water holds under 68. BWOs return in mid-September, and October caddis are rarely seen.