By Evin Oneale, Idaho Department of Fish and Game
Lost Valley Reservoir, west of McCall, will soon be dried up by irrigation demands, and Idaho Fish and Game plans to take advantage of that to improve trout fishing.
A large population of yellow perch now lives in 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 said. "The perch can never grow to acceptable size for anglers, and by consuming nearly all of the available food supply in the reservoir, perch limit growth of the trout stocked by Fish and Game each year."
Trout fishing is also made more difficult by perch that quickly eat bait intended for trout. The reservoir drawdown will accomplish part of the remedy.
"Most of the perch will be removed from the reservoir as it is drained," Janssen said. "However, a significant number of perch will remain in the small storage pool above the dam and in Lost Creek and its tributaries."
In early to mid-October, Fish and Game plans to kill the remaining perch in these areas above the dam and in the plunge pool below with rotenone, approved by the federal Environmental Protection Agency, but it is not poisonous to humans.
"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 said. "However, those fish are likely to perish anyway with no water flowing from Lost Valley Reservoir."
The entire process should be completed within a 24-hour period, and anglers will see 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 has been treated with rotenone eight times since 1959 to remove yellow perch and improve the trout fishery," Janssen said. "These other treatments have resulted in an improved trout fishery, but the effects have been short lived because of 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.
Evin Oneale is the regional conservation educator in the Southwest Region.