Nutrient Removal (Alum Treatment)

As in other urban lakes, Lake McCarrons suffers under excessive nutrient loads that accelerate algae growth and reduces its ecological health and recreational value. Pervasive algal blooms lead to cloudy water, noxious odors, and depletion of dissolved oxygen which can lead to fish kills. The primary external source of phosphorus to Lake McCarrons is polluted stormwater from the watershed: runoff that contains fertilizer, leaves, and grass clippings.

In October 2004, a 500-ton treatment of aluminum sulfate (alum) was applied to Lake McCarrons in order to improve lake water clarity. In these types of treatments, alum is applied to all areas of the lake with a depth greater than 5 feet using a boat and barge with spray attachments. After it is sprayed, the alum immediately bonds with phosphorus present in the water column. The bonds appear in the form of a non-toxic, white floc which descends to the bottom of the lake. The floc remains chemically stable and keeps the phosphorus unavailable for algae overgrowth. The floc also creates a chemical barrier to phosphorus particles adhered to the sediment at the bottom of the lake.

The cost of the 2004 Lake McCarrons alum treatment project was approximately $90,000.