Henrys Fork
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Henrys Fork (also called the Henrys Fork of the Snake River) is a tributary river of the Snake River, approximately 110 mi (177 km) long, in southeastern Idaho in the United States. It drains the northeastern corner of the Snake River Plain along the continental divide. Henrys Fork is named for Andrew Henry, of the Missouri Fur Company, who first entered the Snake River plateau in 1810. He built Fort Henry on on the upper Snake River, near modern Rexburg, but abandoned this first American fur post west of the Rocky Mountains the following spring.
The river rises out of Henrys Lake, west of Targhee Pass on the continental divide on the border with Montana. The Henrys Lake outlet is subject to substantial draw-downs from irrigation diversions during the summer. Late in the season, as the draw-downs decrease with the cooler weather, more water is released into the stream, allowing fish to move up from the lower section of the river. There is a Nature Conservancy learning station near the outlet stream.
South of the lake at Big Springs, nearly 500,000 U.S. gallons (1,900 m³) of constant 52 degree Fahrenheit (11 °C) water flow into the river each day. The river flows south through a high plateau in northern Fremont County, through the Caribou-Targhee National Forest, and passes through Island Park Reservoir. Emerging from Island Park Reservoir, the river flows through a canyon that then opens up into a broad, flat meadow located in the Island Park Caldera in central Fremont County. The river flows slowly past the town of Island Park, through the Harriman State Park, otherwise known as the "Railroad Ranch", and then descends swiftly as it approaches the wall of the caldera, flowing over both Upper Mesa and Lower Mesa Falls, and emerges from the mountains onto the Snake River Plain near Ashton. It flows southwest across the plain, past St. Anthony, splitting into multiple channels into a broad inland delta north of Rexburg. It receives the Teton River from the east approximately 5 mi (8 km) west of Rexburg. It joins the Snake from the northeast approximately 10 mi (16 km) southwest of Rexburg.
Its headwaters are within 10 mi (16 km) of the headwaters of the Missouri River (on the Red Rock River and Madison River), located across the continental divide in Montana. Island Park Reservoir is used for irrigation in the Snake River Plain. It drainage provides one of the most important rainbow trout fisheries in Idaho in terms of habitat, fish populations, and use by anglers. The section of the river between Henrys Lake and Big Springs is a major spawning area for trout and is closed to fishing.
Henrys Fork has long been noted for its superb fishing, especially its dry fly fishing. Bing Lempke, a pipefitter from nearby Idaho Falls, was considered the local dean of the fishery, until he died in 1990.[1]
