Layer aeration (U.S. Pat. 4,724,086) can be described as a depth-discrete artificial circulation technique. Like destratification, it uses both photosynthetic and diffusional sources of oxygen to overcome oxygen demand. Like hypolimnetic aeration, it maintains necessary vertical temperature structure for coldwater fish and zooplankton refugia. Layer aeration alters thermal structure, creating several functional thermoclines, while retaining stratification stability. Persistent metalimnetic anoxia and increased eddy diffusional transport across the thermocline, common problems with hypolimnetic aeration, are overcome by layer aeration.