Public advised to avoid McIntosh Lake in Thurston County due to toxic algae bloom
Thurston County is warning the public to avoid McIntosh Lake due to a toxic algae bloom.
A lab detected a microcystins toxin level of 9.2 micrograms per liter in a sample taken from the lake on July 30, according to the county’s Public Health and Social Services Department. That’s just above the state recreation guideline of 8 ug/L.
McIntosh Lake is off State Route 507 between Tenino and Rainier. The 109.6-acre lake is typically open year-round and frequented by anglers looking to catch rainbow trout, yellow perch, largemouth bass and bullhead catfish, according to the Washington Department of Fish and Wildlife.
People who contact water with high levels of microcystin can develop gastrointestinal illness such as vomiting and diarrhea and suffer liver damage, according to the county’s website. County staff plan to collect and test one sample per week until toxin levels fall below the regulatory guideline for two consecutive weeks.
Until then, the county advises the public to avoid drinking or touching the lake water. That means no swimming, wading, wind surfing or water skiing. Pets and livestock should also be kept away from the lake.
Anglers ought to release any fish they catch during the algae bloom, according to the advisory. The public also should refrain from eating contaminated fish and boating in areas of scum.
A significant algae bloom could be seen at the lake Wednesday morning. The county warns toxins may still be present even if the lake is visibly clear of algae, so it’s best to wait until lab results confirm the microcystins level has improved.
McIntosh Lake is the only lake with a health advisory as of Wednesday. Lab results from July showed microcystins levels at Pattison Lake, Offut Lake, Clear Lake and Lake Lawrence were well below the state recreational guideline.
The public can view current lake advisories on the Thurston County website.
This story was originally published August 6, 2025 at 11:27 AM.
