Complaints of declining water quality and increasing macrophyte growth resulted in a 3-year study to determine the feasibility of phosphorus control on recreationally important Lake Wabamun, Alberta. All nutrient inputs including groundwater were measured or estimated to assess the importance of each source. A preliminary phosphorus loading calculation suggested that the sediment may supply a large quantity of phosphorus during the annual cycle. Sediment release was estimated using a mass balance approach and by phosphorus analysis of sediment cores taken at biweekly intervals. The mass balance suggested that release occurred in late summer, and represented a gross input that exceeded annual external supplies. This was supported by a decline in non-apatite inorganic phosphorus in cores during the same time. These results led to the conclusion that major phosphorus control projects in the watershed were not warranted.