Spot checking the stratification pattern existing within a power reservoir generally consists of a single series of oxygen and temperature determinations taken vertically at the point of maximum depth. The point of maximum depth ordinarily is found immediately upstream from the impounding structure. Data secured from a series of observations in the John H. Kerr Reservoir, Virginia, are presented which confirm Ellis' warning of 1936 that reservoir stratification in the immediate proximity of a power dam is very unstable and samples collected therefrom may yield entirely different results from samples taken at the same depth but beyond the limits of the adclaustral zone. When determining the stratification pattern within a power reservoir, a series of vertical profiles is indicated. These observations should be spaced along the inundated stream bed as closely as circumstances will permit. When only a single profile is possible for determining the stratification pattern, that profile should be secured at a considerable distance from the impounding structure.