Pinto Lake Alum Treatment Begins April 3

From the City of Watsonville, HAB Aquatics: The City of Watsonville and HAB Aquatics, LLC will treat Pinto Lake with alum Monday, April 3rd-Friday, April 7th. The alum treatment is part of a State Water Resources Control Board 319 (h) Non-Point Source Pollution grant to address the problematic algal blooms. The City Park will remain open during treatment. We kindly ask the public to keep a safe distance from the alum boat and equipment.

Background: During the summer and fall, Pinto Lake develops toxic algal blooms caused by cyanobacteria, commonly referred to as blue-green algae. Cyanobacteria dominate the lake’s aquatic ecosystem, severely impairing water quality, aquatic habitat and recreational activities. The lake’s cyanobacteria also produce toxins with potentially significant human health effects. Cyanobacteria are an emerging water quality concern in the United States and other countries.

After an extensive research effort by staff, it was determined that applying alum to Pinto Lake would be an effective management measure in controlling cyanobacteria blooms. Alum is commonly used to treat drinking water and has proven to be both safe and effective.

In addition to treating the lake, the grant provided funding for controlling sources of phosphorous coming to the lake from the watershed. The primary source of watershed phosphorous is erosion of phosphorous- rich soils. The City partnered with the Resource Conservation District of Santa Cruz County (RCDSCC) and the County of Santa Cruz to implement best management practices in the County Park. The most successful of the sediment control practices have been implemented on the disc golf course at Amesti Creek. The City is continuing to work with surrounding landowners, through the RCDSCC, to implement additional erosion management practices as part of the grant.

After alum treatment, the City will continue to monitor for cyanotoxins and other key water quality parameters. The City is hoping to see an immediate impact on clarity in the lake and a reduction in algal scums and mats on the shoreline and a reduction in toxicity this summer. Post treatment the City will continue to work with stakeholders and partner agencies in the watershed to implement best management practices to reduce nutrient and sediment loadings to the lake.

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