WATSONVILLE — A team of technicians arrived at Pinto Lake City Park on Monday, where they prepared for a treatment city leaders hope will help clean what has been called one of the most polluted lakes in the U.S.

Pinto Lake earned its reputation due to high concentrations of microcystin, a toxin caused by cyanobacteria, commonly referred to as blue-green algae.

Cyanobacteria flourish in the lake thanks to the phosphates running off from agriculture and residential uses, and from erosion of riverbanks.

The technicians today will begin to treat Pinto Lake with aluminum hydroxide, a chemical that will bind onto the phosphates that feed the algae.

The algal blooms have forced city officials to close the lake on several occasions.

Microcystin is harmful to people and animals, causing skin rashes, nausea, diarrhea and liver and kidney damage. It has been linked to several otter deaths in the Pajaro River watershed.

The aluminum sulfate will permanently bind to the phosphates that feed the algae, forming a slurry that will sink to the lake bottom and prevent more phosphates from escaping, said John Holz of HAB Aquatic Solutions, the company doing the treatment.

The original March start date was pushed back after heavy rains caused the lake to flood.

The treatment is funded by a $750,000 grant by the State Water Resources Control Board.
Holz estimated the treatment will take about 10 days.

It does not make the water dangerous, and is safe for the plants and animals that call the lake home, Holz said.

The grant will also fund projects that help stop phosphorous from coming to the lake from rivers and streams.

Sediment control practices have been implemented on the disc golf course at Amesti Creek, and Watsonville is working with landowners to implement additional erosion management practices as part of the grant.

After the alum treatment, the city will continue to monitor the lake.

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