Greenfield is the first city in Iowa to warn residents against drinking its water, fearing contamination from toxic blue-green algae.
But it won't be the last, environmentalists say.
Dozens of Iowa cities and towns rely on lakes, rivers and reservoirs at risk for cyanobacteria — or blue-green algae — to source their drinking water.
Tests on Greenfield's water came back clean for toxins Wednesday, enabling officials to lift a bottled-water order.
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"We know that there are a lot of places that are vulnerable," since runoff from farms and cities more easily makes its way into surface water used for drinking, said David Osterberg, co-founder of Iowa Policy Project, a research group based in Iowa City.
The group released a report last month, saying blue-green algae blooms are becoming more prevalent in Iowa lakes and rivers.