Lake Erie, once a success story about how a polluted lake can be brought back to life, is once again struggling to survive.

During the summer months, the most southern of the five Great Lakes is smothering under huge blooms of green algae, often thousands of square kilometres in size.

A new report to be released by the International Joint Commission (IJC) this Thursday recommends some immediate steps to save the lake.

The acting Canadian chair of the IJC, Gordon Walker, told the House of Commons environment committee that Lake Erie is in a crisis.

"Something has happened," he told federal MPs. "It was all right 10 to 15 years ago, but not now."

That "something," according to Walker, is phosphorus from agricultural fertilizers getting into the lake.

Phosphorus was a problem that many people thought had been solved in the mid-60's.

Canadian researchers discovered that phosphorus in laundry detergent was turning lakes green with algae.

The phosphorous feeds the algae, which absorb the oxygen in the lakes and create dead zones. 

In 1972, the U.S. and Canada signed the Great Lakes Water Quality Agreement, which committed them to take action.

That included banning phosphates from all laundry detergent. Within 10 years the levels of phosphorus had dropped and the lakes were on the mend.

But in 2011, a 5,000-square-kilometre algal bloom in Lake Erie was a sign of more trouble. It prompted the IJC to launch a study into the problem.

Agricultural and lawn fertilizers reaching the lake

The report concludes that phosphorus is getting back into Lake Erie from agricultural fertilizers used in growing corn for ethanol and other crops. Domestic lawn fertilizers are also a source of the phosphorus, said Walker.

"Every home wants to have it on their front lawn, he said. "It all runs into the river and it's untreated and that becomes a problem."

The report says rivers in Indiana and Ohio that flow into Lake Erie are the largest sources of phosphorus, but some of it also comes from Ontario's Grand and Thames rivers.

"We have our problems in Canada, in Ontario but they're not nearly the same degree of a problem that we see over in the U.S. states," said Walker in an interview with CBC News.

The report, called A Balanced Diet for Lake Erie, recommends the lake be declared "impaired," which will trigger action under the U.S. Clean Water Act. In Canada that designation serves as a recommendation for action to the federal and Ontario governments.

The report also recommends that both countries ban the use of fertilizers on frozen fields and increase the amount of protected wetlands that serve as a natural filter.

For Walker, a disturbing lesson from Lake Erie is how quickly an ecosystem can deteriorate.

"I was a commissioner on IJC in the 1990s, and that point in time we held up Lake Erie as the poster child around the world. It was huge, it was beautiful, it was a restored lake, with the greatest recreational  and commercial fishing in the world. Now I come back on the IJC 20 years later and look what we find — a lake that is imperilled."