WATSONVILLE — Efforts last month to clean Pinto Lake have been successful, Watsonville Environmental Projects Manager Jackie McCloud said Wednesday.
The lake has for years been plagued with naturally occurring toxic cyanobacteria, so much so that officials have closed the lake on several occasions. At other times, boaters are warned to avoid contact with the water.
In early April, Minnesota-based HAB Aquatic Solutions treated the lake with aluminum hydroxide, a chemical that bound onto the phosphates that feed the algae. The chemical is safe for wildlife and people, and is considered “food-grade,” a company official said.
The treatment was funded by a $750,000 grant by the State Water Resources Control Board.
The first test results, which came back this week, show a “significant reduction” of phosphates, McCloud said.
“What we have done is effectively cut out the nutrients,” she said. “The alum did exactly what we wanted.”
Cyanobacteria flourish in the lake thanks to the phosphates running off from agriculture and residential uses, and from erosion of riverbanks.
The bacteria produce toxins that are harmful to people and animals, causing skin rashes, nausea, diarrhea and liver and kidney damage.
While the test results are encouraging, the phosphates from eroding riverbanks – and from fertilizer use – will still run into the lake and eventually render the alum ineffective, McCloud said.
Solving that problem, she said, will require cooperation from the people who live and work along the watershed.
City and county officials are planning four outreach events over the next six to eight weeks encouraging such things as sediment control and expeditious use of fertilizer.
“In the long term this will be more difficult,” McCloud said. “We all have to be part of the solution to make it last and be effective.”