Springfield, IL (WAND) – The City of Mattoon has issued a “Do Not Drink” advisory for all residents connected to the city’s water supply after tests revealed the presence of microcystin, a harmful algae toxin.

According to officials, samples taken from the Mattoon Water Treatment Plant detected microcystin levels at 0.35 parts per billion (ppb)—exceeding the state’s advisory threshold of 0.3 ppb. The toxin is linked to harmful algal blooms and can pose serious health risks if consumed.

Residents should not drink tap water, only use bottled water for drinking, preparing food and baby formula, brushing teeth, washing dishes, and making ice. They should also not attempt to treat the water. Boiling, freezing, filtering, or adding disinfectants will not remove the toxin.

According to our news partners at WAND-TV people are urged to continue to use bottled water until further notice.

In an advisory, the city said it will notify the public once tests confirm that the water is safe to drink again.

Sarah Bush Lincoln Hospital posted on Facebook writing, “Even though Mattoon water is unsafe for use, Sarah Bush Lincoln is fully operational and safe for patients, visitors and staff. We are using an alternative water source and have flushed our system to ensure safety and cleanliness.”

This advisory was issued on July 10, 2025, and remains in effect until further testing clears the water supply.