Schmidt’s stability concept is used in a comparison of profiles of temperature and salinity for six meromictic lakes in 1953–4958 and 1972. The dual control of density in these lakes is emphasized by distinguishing “thermal” from “chemical” (or “meromictic”) stability. A slight modification of the Schmidt equation is made to yield a plot with depth of the minimum work required for destratification. Significant erosion of the salinity stratification has occurred in nearly all those lakes investigated, with consequent decreases in stability. Soap Lake, in the Lower Grand Coulee, has been considerably modified by dilution; one effect has been to prolong the existence of meromixis by at least 20 years.