This study investigated possible factors inhibiting spawning of largemouth bass (Micropterus salmoides) in Victor Braunig Lake, a 547 ha power plant cooling reservoir in Bexar County, TX. Data on water quality, fish communities, pesticide and heavy metal concentrations and largemouth bass blood components and sexual development were analyzed from Braunig Lake and Calaveras Lake, a similar power plant lake nearby. All factors were similar between the 2 lakes. Largemouth bass from Braunig Lake began spawning 2 days after being moved to hatchery ponds. Largemouth bass from Calaveras Lake which had a normally reproducing popUlation failed to spawn in pens in Braunig Lake. Braunig Lake largemouth bass had no chronic abnormalities that would inhibit spawning. Fertilized largemouth bass eggs collected from a private lake hatched in Braunig Lake water and healthy fry were produced. Largemouth bass fry collected from the same lake also survived and healthy fingerlings were produced. Injections of chorionic gonadotropin failed to induce spawning in either Braunig or Calaveras Lake largemouth bass held in Braunig Lake. Reproductive failure was apparently not due to poor water quality, overabundance of other fishes, parasite infestations, unusual blood components, pesticide or heavy metal contamination, spawning substrate deficiencies or egg or fry mortality. The exact cause of the spawning repression was not identified. However, this study examined many factors associated with reproductive failure in largemouth bass and demonstrated a potential problem facing fishery managers of power plant lakes. In reservoirs where spawning does not occur, supplemental stockings will be necessary to sustain largemouth bass fisheries.