South Twin Lake (Deschutes)
Reachcode: 17070301000912 | Area: 102.7 acres | Shoreline: 1.4 mi | View on Interactive Map
(From Atlas of Oregon Lakes, Johnson et al. 1985) North and South Twin Lakes are two of the many high country lakes in the Deschutes National Forest that are easily accessible from the Cascade Lakes Highway. They lie east of the Deschutes River, which at this point is the north arm of Wickiup Reservoir. Both lakes are nearly circular, about one-half mile in diameter, and are of volcanic origin. South Twin Lake formed when rising magma within the earth's crust came in contact with groundwater. The resulting explosion created a crater which later filled with water. There is no surface inflow or outflow to or from the lake; water enters by seepage and direct precipitation, and is lost by seepage and evaporation. Hydrologic retention time is estimated to be 22 years, one of the highest for lakes in this study. Maximum depth is nearly 60 feet and the bottom drops off steeply from the shoreline, leaving very little shallow water.
The Twin Lakes have long been noted for fine fishing. In 1940, former President Hoover visited the lakes for this purpose. However, the history of fishing success has been off and on. South Twin Lake was the first in Oregon to be treated for scrap fish (1941); the treatment was a success and served as a model for other lakes. Unfortunately, chubs were reintroduced and the lake has had to be treated several times since. Nevertheless, it remains a good trout lake and continues to receive heavy use from anglers. A resort on the shore has new and rustic cabins and a lodge that offers supplies and rents boats. On the north shore is a Forest Service campground. No motorboats are allowed on the lake.
Water quality in South Twin Lake is unusual. Concentrations of major ions, alkalinity, and conductivity are well above average for mountain lakes of the Cascades, although slightly less than in nearby North Twin Lake. Sodium, potassium, calcium, and magnesium concentrations are second only to North Twin Lake among the Cascade lakes in this survey. The pH is also above average, phosphorus concentration is moderate, and chlorophyl concentration is low. Water transparency, although high, is slightly less than in North Twin Lake. The survey of 7/19/82 supported the findings of an Oregon Department of Fish and Wildlife survey in 1940 which also found the lake to have some unusual characteristics (Newcomb 1941). Temperatures were 65.1° F. (18.40 C.) at the surface, and 46.6° F. (8.10 C.) at the bottom on 9/6/41, and there was a thermocline between 15 and 25 feet. Enough oxygen to support trout was found at 17 feet, less than 5 ppm from 17 to 25 feet, and none below 25 feet. The lower water contained 40.0 ppm of carbon dioxide, and was acid in reaction, while water above 25 feet was alkaline. The bottom deposits contained the lowest number of invertebrate organisms of any of the 40 Deschutes National Forest lakes surveyed in 1940. Low oxygen and high carbon dioxide might indicate oxidation of large amounts of organic matter in the hypolimnion, or the presence of mineral springs, which are not uncommon in this area of recent volcanism. The surface waters show no evidence of excessive enrichment and no macrophytes grow in the lake. Dinobryon divergens is present, indicating low phosphorus content. Water transparency and chlorophyl concentrations indicate that South Twin Lake is oligotrophic. However, the oxygen profile, major ion and phosphorus data identify the lake as generally mesotrophic.