Press Release

Lost Valley Reservoir Trout Improvement Project Planned

Lost Valley Reservoir, located 16 miles north of Council Idaho, is nearly dry and Fish and Game plans to take advantage of that condition to improve trout populations at the popular fishing hole.

The Lost Valley Reservoir Company has lowered the reservoir to the lowest pool possible for outlet valve repairs and is cooperating to keep the pool down until later in October.

A large population of yellow perch now occupies the reservoir, effectively limiting the growth of rainbow trout stocked by Fish and Game. “Lost Valley is simply too small to support a quality yellow perch population,” Fish and Game fisheries biologist Paul Janssen noted. “The perch can never grow to acceptable size for anglers and by consuming nearly all of the available food supply in the reservoir, perch also limit trout growth.” Trout fishing is also made more difficult by perch that quickly consume baits intended for trout.

The reservoir drawdown is the first part of the remedy for this situation. “Most of the perch left the reservoir as it was drained,” Janssen said. “However, a significant number remain in the small storage pool above the dam and in Lost Creek and its tributaries.”

A fish salvage operation will be a second part of the remedy. Lost Valley Reservoir will open to salvage fishing on September 30, a declaration that allows fish to be harvested by anglers using any method except firearms, explosives, chemicals or electric current. All size and limit restrictions are suspended during the salvage, but no live fish may be transported from the reservoir. The salvage order closes on October 22.

Creative Commons Licence
Evin Oneale, IDFG

In late October, Fish and Game staff will remove the remaining perch from above the dam and in the plunge pool below the dam using a five percent rotenone concentrate (an EPA-approved chemical fish toxicant). “The reservoir outlet will be closed just prior to treatment, but we anticipate some leakage of rotenone-laden water out of the reservoir outlet that could kill fish in Lost Valley Creek, possibly down to its confluence with the West Fork of the Weiser River,” Janssen noted. “However, those fish are likely to perish anyway with no water flowing from Lost Valley Reservoir.

Rotenone is non-toxic to mammals and presents no harm to humans in the concentrations used. Most of the chemical will be applied by a licensed crop duster-type airplane, and the entire process should be completed within a 24-hour period. Because the reservoir will begin refilling immediately following treatment, rotenone toxicity should be diminished in about a week.

The beneficiaries of all this effort are Lost Valley anglers who will see much improved trout fishing for the next four to five years.

The treatment of Lost Valley Reservoir to remove yellow perch is an old story. “Lost Valley was last treated five years ago for the same reason, and has been treated with rotenone ten times since 1959 to remove yellow perch and improve the trout fishery,” Janssen said. “Past treatments have resulted in an improved trout fishery, but the effects have been short lived due to subsequent illegal introductions of yellow perch and the difficulties associated with removing all the yellow perch during a treatment.”

To learn more or to comment on the proposed treatment of Lost Valley Reservoir to improve trout fishing, contact the Fish and Game McCall office at 208-634-8137.

- IDFG -