The Portneuf River drains a watershed of more than 2100 square miles as it flows from its headwaters on the mountains of the Fort Hall Indian Reservation (above Chesterfield Reservoir) through Lava Hot Springs to Pocatello and back onto the Fort Hall Indian Reservation by American Falls Reservoir. Here the Portneuf River flows into the Snake River. The Portneuf River Watershed includes Marsh Creek, which flows from Downey to Inkom, where Marsh Creek joins the Portneuf River.
Once a blue ribbon cutthroat trout fishery, today the Portneuf is in need of restoration to bring back this fishery to its full potential and enable greater community enjoyment of the river. Community groups are actively involved in researching the river’s health, monitoring water quality and engaging in millions of dollars’ worth of restoration activities.