Hatch and Panguitch, the upper valley
The Sevier begins just above Hatch where Mammoth and Asay Creeks come together, then runs north beside US-89 through the Panguitch valley. Local guides call it the longest north-flowing river contained in a single state, and north is the direction it runs the whole way. The upper valley river is a small meadow stream through ranch land, reached at the highway bridges; the tributaries here (Mammoth Creek, Asay Creek and Panguitch Creek below Panguitch Reservoir, a Blue Ribbon stream) have more public access and are where the Panguitch-area guides spend their time.
Circleville Canyon to Circleville and Kingston
North of the Panguitch valley US-89 drops into Circleville Canyon, the best-known main stem trout water, with pullouts along the highway. Below the canyon the river crosses Circle Valley past Circleville and picks up the East Fork near Junction and Kingston, then enters Piute Reservoir. The USGS gauge on this page sits in this valley reach above the reservoir, where irrigation takes most of the river in summer.
Piute Reservoir tailwater
Below Piute Dam, north of Junction, the Sevier turns into a tailwater. Circle Valley Anglers, the local outfitter, fishes the 24 miles from the dam down to the Clear Creek confluence near the town of Sevier and calls browns, rainbows and cutthroat abundant there. There is no USGS gauge on this reach, so the Kingston gauge upstream is only a rough guide to it; dam releases are what matter.
East Fork Sevier
The East Fork comes in from the Bryce Canyon country by way of Antimony and Kingston Canyon, not from Cedar City, which is well to the west on the far side of the Markagunt Plateau. The Utah DWR bought stream access here in the 1990s and 2000s, and the roughly nine miles of Kingston Canyon and six miles of Black Canyon below Antimony are Blue Ribbon water that produces the largest trout in the drainage. Black Canyon from the BLM boundary up to Deer Creek is artificial flies and lures only.
Trout
Wild brown trout are the backbone of the whole system, with rainbows, cutthroat, whitefish and a few brook trout in the East Fork headwaters. Fish run smaller than northern Utah's big rivers and the East Fork canyons hold the exceptions. Spring runoff and summer irrigation both shrink the river, so late spring and fall are the reliable windows.
Season and regulations
The Sevier is open all year. At the Kingston gauge USGS monthly means run about 150 cfs from November through March and fall to roughly 40 cfs from July into September as diversions take the water, so this page treats 50 to 200 cfs as the fishable band for the valley reach and anything under 50 as a sign the river is mostly in the ditches. Runoff in April and May can double the winter numbers and muddy the canyon.
The main stem carries Utah's general trout rules (statewide daily limit of 4 trout, bait allowed). Special rules apply on the East Fork: artificial flies and lures only from the BLM boundary south of Antimony upstream to Deer Creek, and the feeder canal to Otter Creek Reservoir is closed January 1 to the second Saturday of July. Much of the valley river is private ranch land, so use bridges and marked DWR access. Check the current Utah fishing guidebook before you go.