Fish kills typically occur at times of sudden complete whole-lake mixing following a period of extended stratification. During periods of stratification – during summer months or under ice during winter – bottom waters can become depleted of dissolved oxygen (DO). Under these anoxic conditions, hydrogen sulfide (H2S) can accumulate in bottom waters. Both anoxic waters and H2S are toxic to fish. If the volume of anoxic water is relatively large, a fish kill can occur when a pond or lake completely mixes (e.g., fall turnover, spring turnover, or a summer storm event). SolarBee circulation can help prevent fish kills by preventing blue-green algae blooms (whose death and subsequent decomposition are a major cause of bottom water DO depletion), and by improving the distribution of DO throughout the water column.