North Tenmile Lake
- Coos County
- Douglas County)
(From Atlas of Oregon Lakes, Johnson et al. 1985) North Tenmile Lake is a large natural lake on the Oregon coast south of the mouth of the Umpqua River. It is part of the well-known "Tenmile Lakes" system which includes the larger Tenmile Lake immediately to the south. The lakes are named for Tenmile Creek, which connects them to the ocean. The creek was so named because it was thought to be about ten miles south of the pioneer settlement at Winchester Bay. The geological development of these lakes from an old stream system is described earlier in this volume in the Tenmile Lake report. North Tenmile Lake shows a distinctive dendritic, or branching, pattern characteristic of lakes formed in submerged river valleys. Surface streams enter at several arms of the lake and the outflow is into a navigable channel leading to Tenmile Lake about half a mile away.
Most of the shoreline property around North Tenmile Lake is privately owned and some small water rights exist for domestic use and irrigation by local land owners. Timber companies own most of the land throughout the drainage basin, much of which was logged off in the 1940s. Brush and second-growth timber now cover the hills in this part of the Coast Range. North Tenmile Lake receives heavy recreational use, particularly by fishermen, although not as much as Tenmile Lake. It is primarily trout water while the other is a bass lake. Bluegill are also found in North Tenmile Lake in great numbers. In some years coho salmon run up Tenmile Creek to the lakes and provide good angling.
The Tenmile Lakes are later in their geological stage of development than Clear and Eel Lakes, which were part of the same ancestral stream system. Clear and Eel are deeper with relatively steep shorelines. North Tenmile is a shallow lake with a mean depth of 11 feet and is gradually filling in with nutrient-rich sediment from the drainage basin. Narrow marshes border much of the lake and the bottom is composed of sand, muck and peat. There are dense growths of rooted macrophytes, including the genera Brasenia nuphar, Typha, Potamogeton, Myriophyllum, and particularly Elodea which was introduced in the 1940s. The long history of problems with macrophytes and fish populations in the Tenmile Lakes is discussed in the earlier report.
Water quality in the two lakes is similar although North Tenmile is slightly more eutrophic, a determination based on concentrations of total phosphorus and chlorophyl, transparency, conductivity and nitrates. The sample taken on 5/5/82 showed a high nitrate concentration. Algal blooms have been noted, particularly Volvox aureus and Melosira granulata. Both Volvox and Asterionella formosa, also commonly found, have been associated with taste and odor problems, indicating the highly enriched state of North Tenmile Lake.