Portneuf River

About Portneuf River

The Portneuf River flows 124 miles from its headwaters in western Caribou County, Idaho, southeast of Pocatello, before emptying into the American Falls Reservoir. This river drains a valley carved by ranching and farming, and it winds its way around the southern end of the Portneuf Range, then turns north. It cuts through the Bannock Range and flows northwest through downtown Pocatello, emerging onto the Snake River Plain. The Portneuf is a tributary of the Snake River and part of the larger Columbia River Basin. Anglers will find it a varied waterway, with sections that are channelized and others that are more open, featuring a mix of banks and structure. Access points are generally good, with roads paralleling much of the river and facilities like campgrounds available in certain areas. The Portneuf River is managed as a put-and-take fishery, with regular stockings of catchable-sized Rainbow Trout. Brown Trout and Cutthroat Trout are also present and can grow to respectable sizes. The river supports a natural insect population, with observed species including Caddis, Stoneflies, and Mayflies like Baetis (BWO). This provides a food source for the resident trout. Effective flies will include standard patterns like Stimulators, Elk Hair Caddis, and Baetis nymphs. When fish are looking up, try a small parachute Adams or a spent spinner pattern. For subsurface action, San Juan Worms and scuds can be productive, especially in slower pools and along deeper banks. Streamer patterns like Woolly Buggers can also entice larger browns and rainbows. Work the water systematically, focusing on deeper pools and runs during lower light conditions, and riffles and shallower edges as the day progresses. Be mindful of other anglers and respect private property when accessing the river.