River Mill Reservoir (Clackamas)

Reachcode: AOL000086 | Area: 59.7 acres | Shoreline: 3.5 mi | View on Interactive Map

(From Atlas of Oregon Lakes, Johnson et al. 1985)  River Mill Reservoir, known commonly as Estacada Lake, is one of a number of power generating facilities on the Clackamas River operated by Portland General Electric. It was formed by damming the Clackamas River in 1911, and is an extremely narrow and steep sided impoundment. This reservoir raises the water level to provide a drop through the power-house turbines; it has practically no storage capacity. A considerable amount of fishing is done on the reservoir, but it is too small and narrow for much pleasure boating. A small park is maintained by Portland General Electric near the dam on the north side. Facilities are for picnicking only, and there is a boat launching area near the park. The name of the reservoir is due to the existence of a nearby sawmill on the banks of the river.

The chemistry of the water in River Mill Reservoir is typical of drainage basins in the Cascades. The concentrations of phosphorus and chlorophyl, and the water transparency suggest mesotrophic ecological conditions. The "phytoplankton" are composed almost entirely of diatoms that grow attached to rocks and other substrates in rivers (periphyton). These algae undoubtedly originate from the inflowing Clackamas River, and indicate that residence time of water in this reservoir is short and also that the reservoir has a low biological productivity.

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