The profound impact of ionic (saline) waste from soda ash production on the density of inflows to, and the stratification regime of, Onondaga Lake, NY is documented. The analysis is based on inflow data reported by Effler et al. 1996 in this issue and on lake monitoring data collected over the 1968–1994 interval. Particular emphasis is placed on characterization of changes that followed closure of the soda ash manufacturing facility. Inflows enriched with the ionic waste have been more dense than the lake surface and entered as underflows, sometimes plunging to the lake bottom. Density differences have been reduced, but not eliminated, following closure of the facility. During the operation of the facility, the lake annually had a significant salinity component of density stratification, spring turnover failed to occur in a number of years, the duration of summer stratification was extended, and reformation of salinity-based stratification in fall was common. A nearly 90% reduction in ionic waste loading from soda ash production has substantially ameliorated these impacts, though some impact continues to be observed from the residual loading. The impacts of ionic waste on the lake's stratification regime have exacerbated the lake's problem of limited hypolimnetic oxygen resources.