Blue-Green Algae Impact Water Safety

Unsightly and unhealthy, fresh water algae blooms are becoming more common.


Photo: Chris Konieczny, KP News

On July 8, Don Thomson found himself posting signs warning residents on Lake Minterwood that the lake was closed. He had just received notification from the Tacoma-Pierce County Health Dept. that recent tests indicated the microcystin level, a toxin produced by blue-green algae, was 40 times higher than what is considered safe.

Thomson, who oversees the lake for the homeowners association, had asked the county to test the water when residents noticed an algae bloom and were concerned. The county will test weekly until the levels fall to a safe range. Thomson said that the homeowners would meet to decide about treating with algaecides.

Much of the water monitoring on the Key Peninsula is focused on the water quality on beaches where shellfish are harvested and with an emphasis on fecal bacterial counts. Blue-green algae can be a health concern in lakes, and the Pierce County Surface Water Management Dept. just received a grant to study climate change impacts on shellfish, which will include looking at the effects of blue-green algae in Mayo Cove that may be affected by blooms in Bay Lake, which drains into the cove.

Blue-green algae are a type of bacteria called cyanobacteria. Blooms can be unsightly and can be a hazard to boaters or swimmers if they decrease water clarity, but it is the cyanotoxins they produce that are a health risk to people and pets if they are ingested. Although some species produce no toxins, some produce microcystins and others produce anatoxin-a. Microcystins are the most common and affect the liver. They are slow to break down in the water. Anatoxin-a is faster to break down in the water and affects the nervous system. It has been blamed on the deaths of several dogs in the past. 

The cyanotoxins they produce that are a health risk to people and pets.

The state established the Washington State Toxic Algae Freshwater Monitoring Program over 10 years ago, according to Lizbeth Seebacher, a wetland and aquatic biologist with the Washington State Department of Ecology Water Quality Program. Samples are taken from the thickest part of a bloom, so measured toxin levels will represent the highest level present in a body of water. The program provides toxin data for lakes, ponds and streams in the state. 

King and Snohomish counties are active participants in the program; counties with lower budgets, according to Seebacher, are less active. Steve Metcalf, communications specialist at TPCHD, said the Pierce County toxic algae program, which is typically implemented in summer months, is subject to funding. There was no program last year but in June 2019 the Pierce County Council approved $77,000 to fund the lake monitoring program for the rest of the year. Funding will also allow the department to increase community outreach about the importance of surface water quality, including at its office in Key Center.

“We chose a system that saves time and money while protecting people and pets,” Metcalf said. “We check lakes and collect samples weekly for species identification. We can do this analysis at the health department. This tells us if the type of algae we find in samples might be harmful. As an added layer of protection, we sample for toxins every other week, which requires we send samples to a lab.”

TPCHD monitors selected lakes in unincorporated Pierce County based on their history of toxic algae blooms. Palmer Lake, Lake Minterwood and Bay Lake are all monitored.

Treating a lake for cyanobacteria requires a state permit and must be done by a licensed provider. Doug Dorling, head aquatic biologist for Northwest Aquatic Eco-Systems, has contracted with both Lake Minterwood and Palmer Lake homeowners associations for treatment. He said that a state permit requires about a 90-day application process and costs $675 annually. 

Treatments cost $100 to $400 per acre, depending on the treatment required. Algaecides are considered safe, but each lake sets its rules about when they will open for use after a treatment. Palmer Lake, which has had treatments in the past, allows swimming 48 hours after treatment, although if there have been elevated toxin levels, that is a separate consideration.

Seebacher said that climate, sunlight and nutrients all affect cyanobacterial growth. “When we have these drier warmer springs, the blooms tend to start earlier and we’re going to have a bad season. When it gets really sunny, blue-green algae get really happy,” she said. Shallow lakes are affected more by both sunlight and temperature than deep ones.

“Toxic algae blooms appear to be increasing worldwide,” said Metcalf. “Experts are working to determine the causes. Many people suspect climate change is at least partly responsible because of the increase in water temperatures and changes in rainfall.” 

Nutrients, especially phosphorus, also contribute to blooms. Those nutrients come from fertilizer, pesticides, and human and animal waste. Seebacher said there is anecdotal evidence that stocking fish may increase blooms due to their waste.

Dorling said that if blooms are not treated, they may last for a few days or for months, depending on the cause. If the cyanobacteria consume all the nutrients, they will die off, but then as the dead organisms sink and decompose, they can release another set of nutrients. “It can be a vicious cycle,” he said.

TPCHD and Ecology recommend the following preventive measures, all geared to decreasing the nutrients flowing into lakes and streams: Reduce the use of fertilizers and pesticides, maintain septic systems, pick up after pets, wash vehicles away from the lake, don’t feed waterfowl, keep livestock away from the water, and plant native plants between yard and water to reduce runoff and prevent erosion.

Pierce County has a Toxic Algae Watch Volunteer Program. Contact Lindsay Tuttle, to learn more. 

For more information, go to the Washington State Toxic Algae Freshwater Monitoring Program website at