KOLOB RESERVOIR — During the summer of 2018, biologists with the Division of Wildlife Resources found three illegally introduced fish species (yellow perch, bluegill sunfish, and green sunfish) in Kolob Reservoir in southern Utah.
All three species pose a threat to the fish that already live in Kolob, particularly the wild trout. The illegally stocked fish will compete with trout for food, which will reduce the growth rate of the trout, leading to smaller fish for anglers to catch. The overall number of trout in the lake will also decrease as the illegally stocked fish prey on younger trout.
Due to competition for food, predation on young trout and downstream threats to native fish species, the DWR has been working with the Washington County Water Conservancy District (WCWCD) to lower the water level in the reservoir in preparation for a rotenone treatment. The treatment, which will remove the illegally stocked fish, is scheduled for Oct. 15 and Oct. 16.
Increased trout limit
To allow anglers to take fish that will be lost when the treatment occurs, in September the DWR lifted fishing gear restrictions and liberalized the trout limit at Kolob Reservoir. Anglers can keep up to eight trout a day until the treatment occurs. The reservoir will be closed to the public from Oct. 14 to Nov. 1. Trout will be restocked into the lake in spring 2019.
The DWR, sportsman organizations and the WCWCD are offering a reward of up to $3,000 to anyone who provides information that leads to the conviction of the person(s) who introduced these fish into Kolob. If convicted, consequences could include paying the cost to treat the lake. The treatment will likely cost between $15,000 and $20,000.
Similar challenges at Gunlock and Quail Creek reservoirs
In 2015, the DWR dealt with a similar issue at Gunlock Reservoir in southwestern Utah. Biologists conducted a rotenone treatment to remove illegally introduced smallmouth bass, which threatened native species downstream in the Virgin River. Today, Gunlock is recovering. It’s currently a thriving sport fishery for largemouth bass, bluegill sunfish and black crappie.
In addition to treating Gunlock and Kolob, the DWR and the Virgin River Program have been contending with illegally introduced smallmouth bass in Quail Creek Reservoir in southern Utah. Fortunately, through the removal efforts of sportsman groups and various agencies, the smallmouth bass population in Quail Creek does not seem to be expanding. The possibility of a rotenone treatment still remains, however.
Illegal fish stocking
Regarding the upcoming treatment at Kolob Reservoir, Richard Hepworth, regional aquatics manager for the DWR, says it’s unfortunate biologists are having to deal with another illegal fish stocking. “When fish are stocked illegally,” he says, “there are tremendous costs and consequences for water users, anglers and visitors. Fish that are stocked illegally also harm the fish habitat and the ecosystems in the waters in which they’re placed.”
According to Ron Thompson, general manager of the WCWCD, this is the second district-owned reservoir — in three years — that will be treated to remove illegally stocked fish.
“Visitation to our reservoirs has increased significantly,” he says, “and we’re happy to see so many guests using and enjoying the reservoirs for a variety of recreational purposes. But we have to remember that the primary purpose of a reservoir is to store the water that’s needed for our residents and businesses. Actions that interfere with this primary purpose are disconcerting.”
If you have questions about the rotenone treatment at Kolob Reservoir, call the DWR’s Southern Region office at 435-865-6100.