|Grays Lake, Caribou Mountains.|
The 20 miles of Willow Creek below Ririe Dam is controlled for irrigation and flood control. Maintaining a wild fishery in this area is only feasible with minimum year-long releases below Ririe Reservoir, although numerous trout from irrigation ditches which flow into Willow Creek via the South Fork Snake River provide a seasonal fishery.
Ririe Reservoir has developed into a very popular fishery only 20 miles from Idaho Falls. It supports one of the most intensive salmonid reservoir fisheries in Idaho. This fishery is supported primarily through hatchery releases of rainbow trout and kokanee salmon. Minor populations of cutthroat and brown trout are also present. Splake (brook trout x lake trout hybrid) and lake trout were stocked in 1993 on an experimental basis to control chubs and suckers and provide another sport fishery. Effectiveness of the introduction is unknown at this time.
Smallmouth bass were introduced into Ririe Reservoir from 1984 to 1986.
The 95 miles of streams in the drainage of Willow Creek above Ririe Reservoir are mainly in narrow canyons and contain important wild cutthroat trout populations. Water flows vary from extremes of several thousand second-feet during runoff to a few second-feet in late summer and winter in Willow Creek.Cutthroat trout in the mainstem areas of Willow Creek and Grays Lake Outlet are dependent on downstream movement from tributary spawning and nursery areas. Most tributaries of Willow Creek contain wild populations of cutthroat, brown, and/or brook trout. Native cutthroat trout populations are presently depressed in the drainage, although thought to remain viable.