Tenmile Lake, Oregon

Tenmile Lake and North Tenmile Lake are lakes formed when the dunes impounded Tenmile Creek creating two connected lakes in the dendritic valleys of the coastal range. The Tenmile watershed was a remarkable spawning and nursery site for coho and secondarily for steelhead and sea-run cutthroat trout. This changed in the 1930s when warm-water species (yellow perch) were first introduced. Over the subsequent decades, additional non-native species were introduced, while simultaneously the native anadromous runs declined precipitously. Within the watershed the valuable timber was harvested, while in the valleys the streams were re-routed to the valley edges leaving the drained former wetlands available for cattle grazing.

With this backdrop, J. Eilers (at that time with E&S Environmental Chemistry, Inc.) was hired to direct studies of the lake and its watershed. A new bathymetric map was produced, sediment cores were obtained from throughout the two lake basins, and flow-based monitoring of the major tributaries was conducted. These data were used to calibrate a watershed model (SWAT) of historical, current, and forecasts of future watershed loads of sediment and nutrients. These products were used by the Oregon Department of Environmental Quality to develop the TMDL for the Tenmile Lakes and its watershed.