For the second day in a row, officials warned the roughly 500,000 residents of Toledo, Ohio, not to drink or use their tap water. Boiling it will only increase the water’s toxicity, and experts say that those with sensitive skin and liver disease shouldn’t even shower. The culprit? An algae bloom in Lake Erie—which was likely fed by fertilizer runoff, sewage, and livestock farms—that has affected the city’s water supply.
“[Harmful algal blooms] occur when excess nitrogen and phosphorus are present in lakes and streams,” according to local TV station ABC 13. “Such nutrients can come from runoff of over-fertilized fields and lawns, from malfunctioning septic systems and from livestock pens.”
A water-treatment plant that supplies the city has been positively tested for microcystin, a toxin produced by blue-green algae that can cause diarrhea, nausea, and liver damage.
Because a good amount of farmland runoff makes its way to Lake Erie’s shallow basin, algal blooms are common. (Phosphorus is a key ingredient in fertilizers.) But scientists are also looking into whether climate change is making things worse.
“Lake Erie continues to experience serious changes as a result of phosphorus loading, compounded by the growing influence of climate change,” according to a 2013 report by the International Joint Commission. “Precipitation patterns in the Lake Erie basin under climate change are characterized by less frequent, but more intense, storms. Such intense events lead to high nutrient runoff from agricultural and urban lands, and increased overall nutrient loads to Lake Erie.”
The National Guard and the Ohio Department of Transportation are delivering water to the area while officials await results from further water testing. Toledo spent $4 million on chemicals to treat its water supply last year, reports USA Today.