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.
The Nature Conservancy sponsors a learning station near the outlet stream. South of the lake at
Big Springs, nearly of constant 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. It emerges from the reservoir and flows through a canyon that opens up into a broad, flat meadow 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, and splits into multiple channels into a broad inland
delta north of
Rexburg. It receives the
Teton River from the east approximately west of Rexburg. It joins the Snake from the northeast approximately southwest of Rexburg, just below . Island Park Reservoir, a component of the
Minidoka Project, is used for
irrigation in the
Snake River Plain. Its drainage provides one of the most important
rainbow trout fisheries in Idaho regarding habitat, fish populations, and use by anglers. The section of the river between Henry's 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. == See also ==