A toxic algae advisory went into effect Thursday for Summit Lake in Thurston County.
Tests on Monday showed anatoxin levels were at 18.126 micrograms per liter, which is over 18 times the advised level, according to Thurston County Public Health and Social Services. Anatoxin is a potent neurotoxin that can cause injury or death.
The warning will stay in place until samples are within normal levels for two weeks.
Blue-green algae is related to bacteria and can be found in bodies of water. Blooms most commonly occur in warmer months when light and temperature create conditions that are prime for growth.
Not all blooms are toxic, but some blue-green algae can cause people to become ill after coming in contact with it. Symptoms include stomach pain, vomiting, diarrhea, or an allergic reaction, such as hives, itchy eyes or throat, or a skin rash.
People are advised to avoid contact with water where the bloom is present and not eat fish from the lake during a bloom.
Residents who get their drinking water from Summit Lake should not consume it, rinse dishes or food, or bathe with it while the advisory is in effect, because filtering or boiling the water will not remove the toxin.
Toxic blooms have been increasing in Washington over the last 25 years, according to Thurston County Public Health.