Briery Creek Lake was stocked with both the Florida and northern subspecies of largemouth bass (Micropterus salmoides floridanus and M. s. salmoides, respectively) at a ratio of 3 Florida to 1 northern bass following impoundment in 1986. Progeny of these stockings in the 1989 and 1990 year classes were sampled in October as age-0 and again the following May and electrophoretically assayed to assign phenotypes for comparison of overwinter survival, first-year growth, and relative weight. Subspecies as well as intergrade (F1 and Fx) phenotypes were present in both year classes. First-generation hybrids dominated the 1989 cohort, but Fx and F1 bass were equally prominent in the 1990 year class. Approximately 50% of examined alleles were of Florida bass origin in both year classes. Differential overwinter mortality occurred among phenotypes in both year classes, with the percentage of the Florida subspecies declining by two-thirds while intergrade bass proportionally increased. First-year growth and relative weight did not vary consistently among phenotypes. The Florida subspecies of largemouth bass is likely to provide at best only a small and short-term direct contribution when stocked in waters experiencing winter thermal regimes like that of Briery Creek Lake (≥100 days <10 C water temperature, >1,900 heating degree days). Potential benefits of Florida largemouth bass introductions to Virginia and states with similar climates may be outweighed by the consequences of persistent contamination of northern largemouth bass gene pools.