Physical, chemical, and biological differences between two similar ponds were studied. One pond was heated to 5 C above ambient temperature, while the other served as a reference. Two hundred and fifty green sunfish, Lepomis cyanellus, were planted in each pond. The young-of-the-year grew at a higher rate in the heated pond. The heated pond permitted Chara to grow year round at an accelerated rate. It produced more oxygen during the day and lost more oxygen during the night than did the reference pond. The latter showed greater annual fluctuations of total alkalinity and conductivity. There was an indication that the synergistic effect of temperature and oxygen with an unlimited food supply will promote fish growth. (Author)