When runaway algae killed fish and fouled beaches in the Great Lakes region decades ago, governments ordered cutbacks of phosphorus — a key algae nutrient — from laundry detergents and sewage treatment plants.
It worked, for a while, but scientists acknowledge there are no simple solutions for a recent algae outbreak that is littering shorelines with stinky muck, and it may be responsible for die-offs of loons and other water birds.
"We've done all the easy stuff," Harvey Bootsma, a University of Wisconsin at Milwaukee scientist, said during a recent conference on Lake Michigan environmental problems.
Another crackdown on phosphorus from sources such as livestock farms and urban lawn fertilizer would help, he said. But there's a catch. While areas near shore have too much phosphorus, some deeper waters don't have enough to support plankton, a crucial link in the food chain. So fish are going hungry.
"We have almost two ecosystems in the lake," Bootsma said. "And we don't have one nice, handy management strategy that will work in both cases."
An even bigger complication is the presence of zebra mussels and their cousins, quagga mussels — invasive species that reached the Great Lakes in the late 1980s. They promote algae growth by filtering water and making it clearer, allowing sunlight to penetrate deeper.
Shoreline algae, known as cladophora, fastens itself to mussel shells and feeds on their waste.
Mussels — and cladophora — have spread across the four lower lakes. Scientists believe the mussels are more to blame for the cladophora resurgence than phosphorus pollution. But no one knows how to get rid of the mussels.
"It looks like our only management option for cladophora is to try to reduce phosphorus concentrations," Bootsma said.
Controlling algae blooms was a leading goal of the Great Lakes Water Quality Agreement between the United States and Canada in 1972. Thick clumps of decaying cladophora were chasing away beachgoers and swimmers, while offshore algae blooms strangled fish by depleting oxygen.
The problem receded, thanks to phosphate detergent bans and changes in municipal and industrial waste treatment. But it returned by the late 1990s and has worsened the past few years.
3,400 birds found dead
Among the likely victims: aquatic birds. More than 2,900 loons, grebes and other species were found dead last November along Sleeping Bear Dunes National Lakeshore in northern Michigan, park biologist Ken Hyde said. An additional 500 have turned up this year.
They had eaten round gobies infected with type E botulism from mussels the fish had gobbled. Bacteria from decaying cladophora helped cause the botulism.
"Divers have found huge beds of cladophora on the bottom offshore where the birds died," Hyde said during the State of Lake Michigan Conference.
Cladophora's comeback illustrates the need to prevent additional exotic species infestations, said Judy Beck, Lake Michigan manager with the Environmental Protection Agency's Great Lakes office in Chicago.
In the meantime, scientists said, more research is needed to gauge the relative importance of phosphorus and mussels to the algae's spread.
Phosphorus concentrations have remained steady or even declined in Lake Michigan's open waters, Bootsma said. But they have risen markedly since 2000 in shallows near Milwaukee. Additional measurements are needed to search for the same trend near shore elsewhere, he said.
Concern about inadequate phosphorus levels harming fish in the open lakes shouldn't deter efforts to reduce phosphorus closer in, said Victoria Harris, a Wisconsin Sea Grant water quality specialist.
Phosphorus in deeper water is mostly recycled and doesn't depend on new infusions from land, she said.
"We ought to be controlling phosphorus for the health of the near-shore waters," Harris said.