Island Lake is a 44 acre lake located five miles southwest of Zerkel in southern Clearwater County. There is an undeveloped public water access located off of the Height of Land Forest Road. Island Lake has been managed as a stream trout lake since 1976. The lake is stocked annually with rainbow and brown trout fingerlings as well as surplus hatchery broodstock of these species when available.
Island Lake contains a population of green sunfish that was first documented in 1996. The abundance of this population has reached a level that is likely interfering with stream trout management in the lake through competition for aquatic invertebrates, which are primary forage items for trout, and rainbow trout in particular. The 2006 population assessment catch rate for rainbow trout (26.33 fish/gill net) was the highest recorded for the lake, with good growth and survival evident from the assessment. At that time the increase in green sunfish abundance did not raise concern for the trout fishery. However, the 2012 assessment documented a dramatic decline in rainbow trout catch rates to 0.33 fish/gill net. The few trout that were captured had not exhibited growth since being stocked the previous fall, and no carryover of fish from previous stockings was documented. Conversely, brown trout are utilizing green sunfish as prey and are exhibiting good survival and growth under these conditions. The 2012 brown trout catch rate of 4.0 fish/gill net was the highest recorded for the lake since brown trout were stocked for the first time in 2002. Brown trout ranged in length up to 17.4 inches, with the majority of the catch in the 13-inch to 16-inch length range.