"These blue-green algae, they're all over the place," said Gary Burlingame, laboratory director for the Philadelphia Water Department. "I can go up and down the East Coast, especially . . . from March to May, and show you where they're growing, just visually, in canals, ponds, lakes, rivers, streams. It's just naturally out there.
"The question isn't 'Where do they grow and where don't they?' " he said. "The question is more 'In what situation do they form a bloom?' "
Lake Erie, which is shallow, offers algae two growth boosters: light and warmth. In addition, the manure that produces bumper crops on the region's farmland and the fertilizer used on lawns rinse into the lake during heavy rains, similarly feeding growth in the algae.
Officials also blame Lake Erie's zebra mussels, an invasive species that eats other algaes, giving the blue-green an edge.
The toxins made by blue-green algae cause abdominal pain, vomiting, diarrhea, pneumonia, liver inflammation, and kidney damage. They're a hazard in recreational waters, too, where skin exposure can be problematic. Additionally, wind can send the toxins airborne, affecting asthma sufferers.
The threat extends beyond Lake Erie, to coastal waters and inland lakes across the nation, officials warn. And they expect it to intensify. They believe climate change's warmer temperatures and heavier rainfalls also played a role in Lake Erie's bloom - and will do so throughout the nation.
"We see the results of excessive fertilizer and manure and the problems they cause in coastal waters, in the Great Lakes, in small inland lakes," said Jordan Lubetkin, a spokesman with the National Wildlife Foundation, which found in a recent report that 21 states issued health warnings related to harmful algal blooms at 147 locations in the summer of 2013.
"It's all related to more intense use of our land," Anna Michalak, a professor of global ecology at Stanford University, said during a recent radio interview.
Nearly two months before the Lake Erie bloom, Sen. Charles Schumer (D., New York) traveled to Buffalo - on the other side of Lake Erie - to urge the federal Environmental Protection Agency to set numeric limits for algal toxins in drinking water and provide more guidance to local water systems.
Nearly 100 of New York's upstate lakes, he noted, have seen blue-green algal blooms.
To better understand the potential for problems, it helps to know a bit about algae.
The world has thousands of algae species, which are important parts of the food web in streams and rivers, said Thomas Bott, research scientist emeritus at the Stroud Water Research Center in southern Chester County.
Normally, the organisms that eat algae keep things in balance. But when light, warmth, and nutrients increase, or grazers can't keep up, you get a bloom.
Many blooms consume oxygen in the water, resulting in fish kills. But when blue-green algae blooms, you have the overlying potential for toxins being present, Bott said.
When a bloom starts, the toxin produced stays inside the algae's cells. But as the algae break down, the toxins are released.
Weirder still, scientists don't yet know why some blue-green algaes produce toxins and some don't.
The troublemaking algae in the Philadelphia region are diatoms, which mainly affect taste and odor. The remedy is to let the algae settle to the reservoir bottom, or filter the water through activated charcoal.
Still, Philadelphia tests for the toxins of blue-green algae about 100 times a year on the Delaware and Schuylkill, its drinking water sources. About 2 percent of the time, the toxin is detected, said Burlingame, of the Water Department, but not enough for concern.
Similarly, Aqua America has seen few problems in its regional water supplies, with one notable exception: Because several ponds on the Neshaminy Creek are known to produce high levels of algae - not the toxic kind, but the kind that produces taste and odor problems - the Aqua plant on the creek now has advanced treatment that includes ultraviolet light.
A spokesman for New Jersey American Water said the company does not face algae issues in South Jersey since its water comes from wells or the Delaware River, "which is constantly flowing and not susceptible to algae growth."
For Abraxis, a Warminster biotech firm that makes test kits to detect algal toxins, the Toledo incident has brought an influx of calls. "For the drinking water community, it was a real wake-up call," said Dave Deardorff, head of sales and marketing.
The kit was used at a recent triathalon in New Zealand, and the results prompted officials to call off the swimming portion.
In addition to professional kits, said CEO Fernando Rubio, Abraxis makes simple dip-stick versions - similar to pregnancy test strips - "for Grandma when she goes to the lake and the grandkids come over."