Silver Lake is empty of people, despite temperatures reaching the 90s over the last week. The water may look clean, but signs posted around the lake warn people to stay out of the water because of a potentially dangerous level of algae toxins.
Cowlitz County health officials posted the signs on July 26, and the announcement has been toxic to recreation at the 3,000-acre lake, which is a popular bass fishing spot.
Silver Lake is no stranger to algae blooms, but the toxin levels aren’t usually high enough to post warnings, according to Season Long, environmental health manager for Cowlitz County Department of Health and Human Services.
“I’m surprised it’s gone on this long,” Long said. “But it has been very hot, which is probably contributing (to algae growth.)”
Silver Lake’s high levels of plant nutrients, including phosphorus, contribute to algae growth, Long said. Lake supervisors say they are working to lower the amount of the nutrient.
The Silver Lake Flood Control District will lower the lake three feet from the top of the lake’s weir on Sept. 10. The main purpose of the measure, recommended by the Silver Lake Advisory Council, is to try flushing phosphorus out of the lake and reduce the algae bloom, council member Gary Fredricks said.
“We’re trying to do something to improve water quality and improve the lake,” Fredricks said.
Algae toxins can be harmful to people and animals if they swallow or come in contact with the water, according to the county health department. Exposure to certain algae toxins can cause flu-like symptoms including stomach cramps, vomiting, diarrhea, and headaches. More serious symptoms like blurred vision, convulsions and severe muscle and joint pain can also occur.
The county health department posted the warning signs at Silver Lake in July after a sample for algae toxins came in above 4.5 micrograms per liter, the “action level” for recreational water.
The department has resampled the lake four times since warning signs went up, Long said. Results from one location remained at 4.8 micrograms per liter, she said. The second site has only been tested once, on Aug. 6, with the latest results showing 5.1 micrograms per liter. Long said even if there is no visible algae on the lake, toxins can still be present.
Long said the last time the department posted toxic algae warning signs at Silver Lake was in 2013. The were up from mid-May to late September, she said.
As soon as results from two tests in a row show the algae toxins below action level, the signs will be taken down, she said. The department will likely replace them with educational signs advising the public to look out for algae and how to report a bloom, Long said.
The algae warning sings have hurt business at Streeter’s Resort, according to owner Brenda Kell. She said this time of year, it’s typical to see people out on the lake, especially in hot weather. No one is on the water now, Kell said.
Looking forward to September’s planned date to lower the lake, Kell said she doesn’t think it will affect business very much.
“The sign impacted us more than what that would impact us,” Kell said. “The lake is already shallow; people are used to that.”
Kell said she hopes people will take the lowering and flushing of Silver Lake as a positive sign that officials are doing something to clean the lake. Time will tell if it has a bigger impact on business, she said.
The advisory council proposed opening the gate in September to avoid impacting public use of the lake, Fredricks said.
The council looked at past studies of similar efforts, but it’s still not clear what the results will be at Silver Lake, Fredricks said.
Weather will be a big factor in the effectiveness of lowering the lake, Fredricks said. If the lake level is already low, there may not be enough water let out when the gate opens to wash out the phosphorus. On the other hand, heavy early September rain may not lower the lake enough to flush out toxins and phosphorous.
Whether the process is effective or not, it won’t cost Cowlitz County citizens extra money, Fredricks said. Other cleaning options, such as dredging, can cost millions of dollars, he said. Dredging involves cleaning out a water bed by scooping out mud, weeds and garbage.
Ken Stone, of the Silver Lake Flood District, said the lake level is down a foot from the top of the weir. With just under a month until the scheduled date to lower the lake, surface levels could drop even more on their own, he said.
It’s unclear now how well opening the gate to flush the lake will work, Stone said. But the process is worth it because it is fairly simple, he said.
“Until you do something like this, you don’t know what benefit it will have,” Stone said. “The learning process will help us decide what to do in the future.”