A toxic blue-green algae bloom in Vancouver Lake prompted Clark County health officials Thursday to warn people to stay out of the water.
It marks the second time in three years a summertime health advisory has been posted at the lake.
“It is especially important to keep children out of the lake because they are more likely to swallow some of the water than adults,” said Dr. Alan Melnick, Clark County’s health officer.
Cyanobacteria blooms have become a relatively routine occurrence in recent years in the shallow 2,600-acre lake.
Lab results from a water sample collected Tuesday revealed 224,000 cells per 100 milliliters of water, well above the World Health Organization standard of 100,000 cells. With a sheen of scum visible in the swimming area, health officials said they began posting warning signs shortly after noon Thursday.
Vancouver Lake Park remained open for picnicking, but parks employees are advising people against water contact.
“Once the color of the pond starts to change, it’s really not an attractive body of water to recreate in,” said Brian Potter, maintenance program coordinator for the Vancouver-Clark Parks and Recreation Department.
Cyanobacteria produce toxins that can cause respiratory illness, rashes and, in extreme cases, kidney and liver damage or death.
Blue-green algae blooms afflict plenty of lakes, but the suspected triggers vary from lake to lake. Those factors include the interplay of sunlight, nutrients, temperature, water flow and the presence of microscopic “grazers” capable of holding blooms in check. The blooms typically occur during warm weather when the water is stagnant.
“Unfortunately, Vancouver Lake has that challenge,” said Tom Gonzales, resource protection program manager for the county health department. “The water’s not moving much.”
Tucked between Vancouver’s city limits and the point where the Columbia River bends to the north, Vancouver Lake has paid the price for man-made changes to the natural environment. The river, harnessed by dams and constricted by dikes, no longer pushes out accumulating sediment with rampaging bursts of springtime snowmelt.
Vancouver Lake is now badly clogged with silt.
At the same time, stormwater collecting everything from fertilizers to motor oil continues to pour into the lake by way of Burnt Bridge Creek and Lake River.
Scientists with Washington State University Vancouver have been studying the lake for the past three years. Ultimately, researchers hope the study will lead to targeted actions to improve water quality.