Limnological characteristics for 1971-1972 of culturally eutrophic Shagawa Lake, Minnesota [USA], were compared to those of the immediately upstream, oligotrophic Burntside Lake to evaluate the effects of domestic waste-water discharge to Shagawa Lake. Typical characteristics of Shagawa Lake were extensive summer blue-green algal blooms (Anabaena and Aphanizomenon), anaerobic hypolimnion and large and rapid fluctuations in chemical constituents. In contrast, oligotrophic Burntside Lake was characterized by low numbers of algae (predominately diatoms and greens), aerobic hypolimnion and small changes in chemical constituents. Chlorophyll a concentrations in Shagawa Lake typically reached 50-60 .mu.g/l while in Burntside Lake the maximum observed was 6 .mu.g/l. Predominant benthic fauna in Shagawa Lake was Chaoborus at densities up to 28 .times. 103 organisms/m2, while in Burntside Lake Amphipoda predominated during the summer as a maximum density of about 1300 organisms/m2. Both inorganic nitrogen (IN) and orthophosphate phosphorus (OP) in Shagawa Lake were depleted to undetectable levels in the epilimnion during the summer. In the epilimnion of Burntside Lake OP was at the detectable limit throughout most of the summer and IN was depleted to undetectable levels. The thermocline in Burntside Lake was relatively stable while in Shagawa Lake it was readily destroyed by passing cold fronts and strong winds, allowing nutrient-rich hypolimnetic water to mix with the nutrient-limited epilimnetic water which helped to sustain the algal biomass.