Lakewood officials have always assumed Fort Steilacoom Park’s former use as a farm by Western State Hospital patients contributed to its lake’s poor water quality.
But they didn’t know until now just how detrimental those practices were.
Waughop Lake has been under a health department-issued “no contact” advisory since 2009 because of its toxic blue-green algae problems.
Lakewood officials assumed over the years that a combination of groundwater runoff, failing septic systems and animal waste contributed to the frequent toxic algae blooms.
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But preliminary information from recent monitoring of the lake shows that isn’t the case.
Instead, it’s the bottom of the 30-acre lake that is the problem.
“The sediment in the bottom of the lake appears to be the big issue,” said Greg Vigoren, Lakewood’s surface water division manager. “That’s what I think they’re honing in on.”
Nearly 65 years of dumping animal manure and other agricultural waste into the lake created a thick layer of nutrient-rich sediment that lines its bottom.
That sediment is the suspected culprit behind the lake’s elevated phosphorus levels, according to preliminary analysis of a year’s worth of monitoring.
The increased phosphorus levels cause the dense aquatic plant growth and plankton blooms that typically happen in the summer when sunlight hits the sediment.
Lakewood officials have always assumed the park’s former use as a farm by Western State Hospital patients contributed to the poor water quality. But they didn’t know until now just how detrimental those practices were.
In their toxic form, blue-green algae can cause illness in humans, pets, waterfowl and other animals that come in contact with the algae, according to the state Department of Health.
Toxic blooms can kill livestock and pets that drink the water. It can also cause skin rashes in humans who come in contact with water and if ingested can cause nerve and liver poisoning, according to the health department.
The city, using grant money from the state Department of Ecology, hired engineering consulting firm Brown and Caldwell and Jim Gawel, University of Washington Tacoma associate professor of environmental chemistry and engineering, to develop a lake management plan.
Part of that plan included monitoring the lake from October 2014 to October 2015.
Precipitation, groundwater and runoff from the shoreline feed Waughop Lake, according to the report. But phosphorus levels in all three sources were lower than the levels found in the lake.
Waughop is a “kettle” lake, which means water doesn’t circulate naturally. Instead it sits in the basin.
Previously, city officials questioned whether stormwater bypassed an infiltration pond on neighboring Pierce College property and flowed into the lake. Untreated stormwater could result in higher phosphorus levels, they speculated.
The sediment in the bottom of the lake appears to be the big issue.”
Greg Vigoren, Lakewood’s surface water division manager
But the consultants determined there is minimal runoff coming from the college, Vigoren said.
Neighboring septic systems southwest of the lake were also ruled out as a source of phosphorus. So too were visiting birds and people who don’t pick up after their dogs near the lake.
The only place left to look was the lake. Sediment samples from the lake bed showed high phosphorus levels.
The consultants continue to analyze the data. When that’s finished, they will evaluate management options for how to handle the toxic blooms.
The city will have to decide whether it wants to treat the water to prevent the algae blooms or let nature run its course.
“Lakes, they become more eutrophic over time. They go from pristine waters to more of a wetland, to a bog, to a grassy area,” Vigoren said. “We have to look at what is going to be the use? And how much cost and effort will it take to get there if we make it better than it is now?”
The city expects to have a final plan for the lake by September.