Decades of excess phosphorus loading to lakes from the watershed often leads to accumulation and burial in the sediment. Under certain biogeochemical conditions, that phosphorus can then diffuse into the overlying water and become available for algal uptake and growth. When internal phosphorus loading from sediments is a large portion of the total load to the lake, that source of phosphorus can sustain algal growth and poor water quality conditions even if external loads are reduced significantly. Consequently, internal phosphorus load reduction is warranted for water quality improvement. Internal phosphorus load reduction using aluminum sulfate (alum) is an effective, well-studied in-lake management technique to reduce phosphorus release from the sediments. This webinar with Dendy Lofton of Stantec and Shannon Brattebo of Tetra Tech will present the fundamentals of alum applications in lakes, advantages and disadvantages of alum, and post-monitoring recommendations to directly evaluate the success of the treatment.