Idaho Fish & Game is preparing to drain Horsethief Reservoir east of Cascade in the fall after someone about five years ago introduced brown bullhead into the lake, which was managed strictly for trout fishing; the trout fishery there was estimated to attract more than 26,000 fishing trips per year and generate $4.5 million a year in economic impact. Brown bullhead is a type of catfish that grows up to 21 inches and is commonly called the “mud cat.”

As the first step in the process, the lake will open to public fish salvage on July 18, a week from Saturday, with all fish bag and possession limits removed. That means people with a valid Idaho fishing license can take fish in any amount by any method, including seines and dip nets, but excluding firearms, explosives, chemicals or electricity. All fish must be killed before they’re transported from the reservoir. The idea is to use most of the fish in the reservoir before it’s drained and treated.

In the fall, after the reservoir is drained to its lowest level, Fish & Game will treat it with rotenone, which is lethal to fish but harmless to livestock, other wildlife, pets and humans. “It’s frustrating to have to spend any sportsmen’s dollars in this manner because of a thoughtless, criminal act by one person,” said Dale Allen, regional fisheries manager for Fish & Game. The ice fishing season for 2015-16 will be canceled. The reservoir will be restocked next spring with rainbow and brown trout.

Fish & Game officials said they began investigating complaints of bullheads in the lake in the fall of 2014, and found a large number of varying ages up to four years. The department said illegal introductions of fish are “extremely costly,” not only to the department, but to local communities and to anglers in lost recreational fishing opportunities.