Dr. Wayne Carmichael of Wright State University and Dr. David Culver of Ohio State University said they are alarmed by the comeback of harmful blue-green algae worldwide, especially one in western Lake Erie called microcystis.
Although it has never been linked to a death in the United States, microcystis has the same toxin in algae that the U.S. Centers for Disease Control linked to as many as 75 deaths in Brazil in 1996.
The two told The Blade recently they support expanding 1998 legislation to include algae research to the Great Lakes, the world's largest body of freshwater.
The stakes for this region go beyond the public health threat of getting too close to any algae that might cluster in a swimming area, the researchers said.
Dogs might lap up tainted water near a shoreline and get sick or die. And the notion of being around slimy algae isn't something that appeals to tourists, they said.
Such poisons can be removed from municipal drinking water fairly easily by carbon filters used by water plants in Toledo and Sandusky. But the devices are expensive - another cost of pollution that can hit people in their pocketbooks, they said.
About the only good that comes from Lake Erie's algae growth is improved walleye and yellow perch fishing. Those fish are light-sensitive, as are some plants in their food web.
With the lake becoming murkier, their numbers have started to increase, Dr. Culver said.
Excessive nutrients are blamed for most algae blooms.
But the Great Lakes mystery goes deeper, because of a drop in nutrients entering streams and waterways since the Great Lakes Water Quality Agreement was signed by President Richard Nixon and Canadian Prime Minister Pierre Trudeau in 1972.
The landmark act, coupled with the federal Clean Water Act that Mr. Nixon signed that same year, led to billions of dollars of improvements at sewage treatment plants.
The laws ordered controls on sewage plants for discharging phosphorus, a natural component of human waste and an element of common fertilizers.
Although researchers at Heidelberg College's water quality lab in Tiffin have documented a steady rise in phosphorus entering the Maumee River and other Lake Erie tributaries, the total still is nowhere near what it was pre-1972.
Much of the increase is believed to be weather-dependent and largely a result of runoff from farms and golf courses, officials say.
That's what makes Lake Erie's steady algae increase a bit baffling.
Lake clarity has decreased from just a few years ago, the result of tiny suspended algae particles.
“We're fairly certain it's directly related to the zebra mussel,” said Dr. Carmichael, who was part of the Centers for Disease Control team that traveled to Brazil to study the microcystis-related deaths.
Those were believed to have stemmed from a system breakdown that allowed toxic algae to pollute water at a kidney dialysis center.
Dr. Carmichael also traveled to China to study similar forms of toxic algae. He recently briefed the House Science Subcommittee on Environment, Technology, and Standards about the problem in the Great Lakes.
Dr. Culver has headed a U.S.-Canada research team studying Lake Erie's blue-green forms of algae.
The algae tends to bloom for about six weeks in late summer, proliferating enough to cluster during those times. Then, they recede and seem almost dormant until the next summer.
But Dr. Culver said he believes Lake Erie's algae problem has been getting a little worse in recent years, after being held in check for two decades.
“Since 1995, the amount of algae in the lake has been increasing every year,” he said. “And the number of years we have gotten [sightings] of blue-green algae blooms has increased.
“We now have algae abundances as high as they were in the early 1980s. A lot of the progress we made by 1990 or so seems to have turned the other way,” Dr. Culver said.
Zebra mussels are voracious filter-feeders. They are among nature's fastest multipliers and were credited for clearing up the murky water in the Great Lakes.
The mussels are suspected of hitching a ride in the ballast water of foreign ships and entering the lake system in the late 1980s.
But a growing consensus among researchers is that the lakes have turned the corner in terms of water clarity and are entering another murky era - largely because of the mussels.
Zebra mussels excrete microcystis and other forms of harmful blue-green algae. In doing so, they essentially re-suspend phosphorus into the water column and alter the ratio between it and nitrogen, which can change the lake's biology and allow algae to grow.
“It has definitely gotten murkier. There definitely is more algae,” Dr. Carmichael said.