Flathead Lake - History

History

Once known as "Salish Lake", this body of water takes its name from the Salish (Flathead) Indians who live at the southern end of the lake on the Flathead Indian Reservation. Kerr Dam, near Polson, regulates the lake's water level and provides hydroelectric power and water for irrigation. The lake has an irregularly-shaped shoreline and a dozen small islands, the largest of which is a state park called Wild Horse Island. These islands cover 5.5 square miles (14.2 square kilometers). Besides the Flathead River, the Swan River (known also as the Bigfork River where it enters the lake) is the lake's other major tributary. The lake is inhabited by the native bull trout and cutthroat trout, as well as the non-native lake trout, yellow perch, and lake whitefish. It is also reportedly inhabited by the infamous Flathead Lake Monster.

The opossum shrimp, Mysis diluviana, invaded Flathead Lake. Lake trout had been introduced 80 years prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m−2 d−1 (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles).