Scientific evidence is sketchy about the causes of massive, smelly algae blooms showing up in most of the Great Lakes, and further study of the problem is needed, researchers contend in a report released last week.

It’s widely believed that phosphorus runoff from farms and municipal waste treatment plants is a leading cause of the algae problem, which has returned with a vengeance after it was considered largely solved decades ago. Climate change and invasive mussels are considered factors as well.

But those assumptions are based largely on observations instead of more reliable scientific experimentation, researchers attest in the report, which was presented during the annual meeting of the International Joint Commission, a U.S.-Canadian agency that advises both nations on issues affecting the Great Lakes and other shared waters.

Joseph Koonce, a Case Western Reserve University biology professor and the co-chairman of the group that wrote the report, said further research is needed to determine the roles of each of the presumed causes.

“We’re dealing with complexities that we don’t appreciate,” Koonce said.

Overabundant algae choked Lake Erie and parts of the other Great Lakes decades ago. The situation improved dramatically after cities improved sewage treatment and laundry detergents containing phosphorus, which algae eat, were banned. But the problem has rebounded in recent years, and scientists say algae covered more of Lake Erie this summer than it has in a half-century.

Dead algae absorb oxygen and create “dead zones” where fish cannot live.

The foul mess washes ashore, chasing away swimmers and beach walkers.

Environmental Protection Agency chief Lisa Jackson announced last week that three watersheds plagued with algae would receive special attention under a Great Lakes restoration program. They include the Maumee River in Ohio, which flows into Lake Erie; the Lower Fox River in Wisconsin, a tributary of Lake Michigan’s Green Bay; and Michigan’s Saginaw River, which flows into Lake Huron.

But there’s disagreement among some scientists and activists about how best to attack the problem. Many are pushing government officials for quick action.

Koonce said without further research, actions might be taken that cause further harm. For example, reducing phosphorus levels too much could leave too little algae at the base of the food chain, reducing fish populations. That’s already happening in Lake Ontario, he said.

via Great Lakes algae problem confounds experts | Green Bay Press Gazette | greenbaypressgazette.com.