An extensive data base of LIDAR and photographically measured plumes from the Nanticoke thermal generating station (located on the north shore of Lake Erie) has been accumulated over several years of full-scale atmospheric experiments. Analysis of the data shows that the empirical entrainment constant used in the Briggs simple plume rise formulation has a value of 0.8, which is significantly larger than 0.6 found by Briggs (1975). A hypothesis is proposed that mesoscale eddies present in the land/lake environment are responsible for vertical plume meander leading to the observed enhanced vertical plume spread and lower mean plume rise at this site. This is substantiated through theoretical considerations and experimental data. The results are significant in the computation of ground-level concentrations at such complex terrain sites.