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Metro Parks plans treatment to curb algae blooms at Wapato Lake

May 1, 2017

Improved water quality to make lake safe for pets, fishing and boating

Metro Parks Tacoma plans to treat Wapato Lake later this spring to reduce public exposure to toxic algae. The blue-green algae blooms can be harmful to people and pets, which has prompted frequent health warnings when weather is warmer.

Wapato Park will be closed on May 9 and 10 for a treatment to protect and improve the lake's water quality. The dog park will be closed and parking may be limited.

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.

After treatment, the 34-acre lake will be closed to the public for one or two days to ensure safety. The plan is to limit problem-causing algae by locking up the polluting nutrient that stimulates its growth. The culprit is phosphorus, a fertilizer that seeps into the lake with runoff from the surrounding landscape. There is also a high legacy phosphorous content in the sediment at the lake bottom.

Keeping Wapato Lake’s water clean has been a challenge throughout the park’s history because the lake is a giant detention basin that fills with such 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.

“Our goal is simple. We want to give visitors to Wapato Lake the confidence that the water safe for people to fish, use non-motorized boats, paddle boards and for kids to dip their toes in,” said Marina Becker, the district’s director of parks and natural resources.

At a public meeting on March 30, members of Metro Parks staff, along with scientific and technical consultants, explained the process, its value and our progress on long-term efforts to minimize pollutants in lake water.

Metro Parks plans to hire 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.

A previous alum treatment – in 2008 – was done incorrectly and killed many fish. To help ensure success this time, Metro Parks has 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 will coordinate oversight with experts from the University of Washington Tacoma, who are also engaged in Metro Parks Tacoma’s long-term plan to improve the quality of Wapato Lake water.

While the treatment takes place, parking at Wapato Park will be limited to the South 72nd Street lot. The Wapato Park dog park will temporarily close. Other off-leash dog parks are located in Point Defiance Park and Rogers Park.

Meanwhile, Metro Parks is advancing 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.

Learn more about Wapato Park and its water.