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Wapato Lake water quality treatment successful

May 11, 2017

Treatment aims to make lake safe for pets, fishing and boating

Metro Parks Tacoma on Tuesday successfully treated Wapato Lake to reduce public exposure to toxic algae.

“We’re happy the treatment went well,” said Marina Becker, director of parks and natural resources for the district. “This should give visitors to the lake confidence that the water is safe for non-motorized boats and paddle boards, and for kids to dip their toes in.”

Metro Parks is working with the state Department of Fish and Wildlife to restock the lake for youth fishing later in the year.

Blue-green algae blooms have been a problem in Wapato Lake in recent years because of the 34-acre lake’s phosphorous content. Phosphorous, fertilizer that acts a nutrient for algae, is present in high amounts in the sediment at the lake bottom and is brought in from the surrounding landscape through runoff.

Metro Parks hired a contractor to disburse alum, or aluminum sulfate, in the water. The alum binds with phosphorus in water and sediment, forming a cap of aluminum phosphate on the lakebed. One application of the treatment is expected to be effective for about five years.

To ensure success, Metro Parks hired Herrera Environmental Consultants, experts with a track record of successful treatment of other algae-plagued Western Washington lakes, including Green Lake in Seattle. Herrera coordinated oversight with experts from the University of Washington Tacoma, who are also engaged in the park district’s long-term plan to improve the quality of Wapato Lake water.

“The water treatment was monitored closely throughout the application,” Becker said.

Keeping Wapato Lake’s water clean has been a challenge throughout the history of Wapato Park because the lake is a giant detention basin that fills with runoff. The Wapato Lake management plan recommends periodic water treatments in addition to utilizing best landscape management practices and working with the surrounding community to improve the quality of stormwater discharged into the lake.

Over the past several years, frequent blooms of blue-green algae in Wapato Lake have produced potentially harmful toxins. Tacoma-Pierce County Health Department, which tracks water quality, has issued intermittent health advisories to warn people and pets to avoid areas of the lake that may have algae.

Meanwhile, Metro Parks is moving ahead with other improvements to Wapato Park, including the replacement of two docks and the addition of a fish cleaning station, new pathways and new benches. The $1.2 million project is funded by the district’s 2014 capital improvement bond measure and a $450,000 grant from the state’s Recreation and Conservation Office and should be finished in 2018.

As with the Wapato Lake treatment, the improvements will occasionally limit parking to the South 72nd lot to allow for construction deliveries. More details will be published on the Metro Parks website as they become available.

Learn more about Wapato Park and its water.