Primary productivity and water quality were studied in Doe Valley Lake, a 147-hectare impoundment on Doe Run, a spring-fed stream in Meade County, Kentucky, from 13 June 1969 to 31 July 1972. Doe Valley Lake is monomictic during most winter seasons, but it is dimictic during more severe winters because of its morphometry and location on the borderline climatic region for dimictic lakes (37 degrees N latitude). Oxygen depletion in the hypolimnion is severe, and anaerobic conditions usually prevail by late June. A hypolimnetic areal deficit of 0.038 mg/sq cm/day was calculated. Super-saturation of oxygen in the epilimnion was common, and metalimnetic maxima exceeded 150 percent saturation in spring and early summer. Primary productivity ranged from 44 to 1,192 mgC/sq m/day and annual rates at Stations I and III were 277 and 255 gC/sq m/yr, respectively. Productivity fluctuated considerably at Station I as a result of turbidity, but average daily rates and chlorophyll levels were higher than at Station III.