Thurston County health officials have issued a public health advisory for McIntosh Lake after detecting elevated levels of a harmful toxin in the water, prompting warnings to avoid any recreational activity at the site.
Recent laboratory testing confirmed that microcystins — toxins produced by certain types of blue-green algae — reached 9.2 micrograms per liter in a sample collected on July 30. This measurement slightly exceeds Washington’s recreational safety threshold of 8 micrograms per liter, according to the county’s Public Health and Social Services Department.
McIntosh Lake, which spans over 100 acres and sits between Tenino and Rainier off State Route 507, is a popular destination for fishing enthusiasts year-round. The Washington Department of Fish and Wildlife lists it as a spot for catching rainbow trout, yellow perch, largemouth bass, and bullhead catfish.
The presence of high levels of microcystin poses serious health risks. According to Thurston County’s health guidance, exposure can result in gastrointestinal distress like vomiting or diarrhea, and in more severe cases, liver damage.
County health staff will now monitor the lake weekly, testing the water until toxin levels remain below the state guideline for two consecutive weeks. Until then, the public is strongly urged not to swim, wade, water ski, windsurf, or have any direct contact with the lake water. Authorities also advise keeping pets and livestock away from the lake during the advisory.
Fishing is also impacted. Anglers are being asked to release any fish caught during the bloom and to avoid consuming fish from the lake during this period. In addition, boating in areas where scum is visible is discouraged.
By Wednesday morning, county staff reported a significant algae bloom was still visible at the lake. However, they caution that even when the surface appears clear, harmful toxins may still be present. Residents are advised to wait for official confirmation that toxin levels have dropped before resuming water activities.
As of now, McIntosh Lake is the only water body in Thurston County under a health advisory. Earlier testing in July showed that other popular lakes, including Pattison, Offut, Clear, and Lawrence, had toxin levels well within safe recreational limits.
For those looking to stay updated, the latest information on lake advisories is available through Thurston County’s public health resources.
