As residents of Toledo, Ohio, and the surrounding region recover from a weekend without access to usable tap water — the fault of a toxic algae bloom in Lake Erie — the crisis has set off new calls for stricter rules on the use the fertilizers that help contribute to the blooms.

The algae bloom set off alarms on Saturday, causing authorities to impose a ban on the use of the city’s tap water, which comes from Lake Erie, affecting more than 400,000 people in Toledo and surrounding areas in Ohio and southeastern Michigan. On Monday morning officials lifted the ban after new tests came back clean. But before the weekend was over, 69 people visited local hospitals fearing they had fallen ill, The Columbus Dispatch reported.

The type of algae found in the lake releases a toxin called microcystin, which can damage the liver and cause diarrhea, vomiting, dizziness and even nerve damage.

“It’s not good to drink,” said Christine Mayer, a professor of environmental science at the University of Toledo.

Mayer said these algae blooms have become more common. And the city’s water treatment plant, she added, wasn’t designed to handle the load. The chief culprit is fertilizer runoff from farms that flows into the Maumee River, which empties into Lake Erie.

For now, federal regulators don’t have a standard for acceptable levels of microcystin. So Toledo officials had to use the World Health Organization’s rule, which states that levels of the toxin should not exceed a minuscule amount.

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