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Eutrophication—the enrichment of ecosystems with chemical nutrients—causes pronounced deterioration of water quality, affecting many of Manitoba’s prairie lakes.

These lakes have deteriorated due to excessive loading of nutrients, organic matter and silt, which in turn cause increased primary producer biomass and reduced water quality. The understanding of eutrophication and its management has evolved from simple control of external nutrient sources to recognition that it is often a cumulative effects issue, requiring protection and restoration of various features of a lake’s community and its catchment.

The success of management techniques varies greatly from lake to lake, where it is generally agreed that these technologies are usually not worth considering unless external nutrient loads can also be reduced and controlled. In-lake remediation techniques can be categorized by limiting and controlling the sediment, or by managing the consequences of lake aging. The techniques described are designed to control nutrients, plankton algae, and other related effects of over-production and species composition changes that result from eutrophication. Algal biomass is dependent on the concentration of the limiting nutrient in the lake’s photic zone; therefore, appropriate evaluation and modelling can determine the feasibility of controlling the primary sources of the most limiting nutrient. More than one technique may be used at once; however, for most in-lake techniques to be effective, important external loading sources should be evaluated and controlled. This review identifies multiple in-lake biological, physical and chemical treatments to limit and control P-enriched sediments and remediate the effects of eutrophication on lake water quality.