"Not every algal bloom will be a toxic one.
But the more algal blooms there are, the greater likelihood you’ll get a toxic one, and one that will contaminate a water supply," Mandelbaum said.
"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.
It points to a 2016 state study that showed 15 of 26 public water systems had detectable levels of microcystins in raw water.
MORE: Iowa nitrogen pollution in the water is getting worse, study shows Cyanobacteria release microcystins as the cell is dying, and the toxins can be dangerous to people when they’re in drinking water.
"The report says cyanotoxins are there," Osterberg said.
The Iowa Department of Natural Resources said the study showed the public water systems’ treatment was effective at removing the microcystins.
Des Moines Water Works, which tests daily for cyanobacteria and microtoxins, issued a warning in 2016 that said microcystins had been detected in finished water, although below health advisory levels.
And he said the state’s Nutrient Reduction Strategy, designed to cut by 45 percent the nitrogen and phosphorus entering waterways and contributing to the Gulf of Mexico dead zone, is not ramping up quickly enough to reduce dangerous blue-green algae blooms in Iowa.