Efforts are already under way to reduce the levels of phosphorus and nitrogen in the lake, said Dwight Williamson, manager of the Water Quality Management Section for Manitoba Conservation.
"We have a pretty good idea now where the major sources are," Williamson said.
Clean-up efforts include educating farmers about the dangers of excess fertilization, protecting natural growth along the Red and Assiniboine rivers to reduce run-off, and talking with officials in American states that contribute about one-third of the nutrients in the lake.
But those initiatives aren't enough, warned Liberal leader Jon Gerrard, noting several Lake Winnipeg beaches were recently posted as dangerous.
"We need some action here," he said. "The NDP for four years have done nothing except put together a committee. The NDP could have started this in their first year in office."
Conservation Minister Steve Ashton announced last February a strategy to cut phosphorus and nitrogen in the lake to the levels of 30 years ago. Ashton was on vacation yesterday and unavailable to comment.
Lake Winnipeg is the fourth largest freshwater lake in Canada and the 11th largest in the world. Manitoba's tourism and fishing industries rely heavily on Lake Winnipeg maintaining a high quality of water.
Williamson noted that, while it isn't yet considered a dead lake, Lake Winnipeg is headed towards life support.
"We're approaching Lake Erie," Williamson said. "It's a lake that is clearly under stress."
Nitrogen and phosphorus occur naturally, and are needed by aquatic life. But, in excess, they cause problems, such as the growth of algae which can starve other plant life of oxygen, and produce toxins.
Last week, two beaches on opposite sides of Lake Winnipeg, Albert Beach and Sandy Hook Beach, were posted as dangerous because of high levels of a toxin called myocystin, which can irritate skin and sicken or kill people who ingest it.
While algae blooms are common on the lake, last week was the first time the toxin levels were considered unsafe.
The toxin levels returned to acceptable levels by yesterday but there is still a warning to look out for large algae blooms and not swim if they are visible.
Two other beaches were posted as dangerous earlier this summer because of high levels of E. coli bacteria.
Gerrard said the government shouldn't wait for the Lake Winnipeg Stewardship Committee, established last month, to study and make recommendations.
He said some action must be taken now, including setting standards for the water quality in all Manitoba lakes and rivers.
He said the lack of such standards was made clear when the Winnipeg north end treatment plant broke down last September and pumped raw sewage into the Red River for nearly four days.
"It didn't break any provincial standards because they're aren't any," Gerrard said.
The federal government fined the city $300,000 under the Fisheries Act but the province couldn't. Instead they called for the Manitoba Clean Environment Commission to hold hearings and force the city of Winnipeg to speed up its water treatment plant improvements.
Williamson said he is expecting clear recommendations from the CEC shortly.
Williamson said other action is underway. He said in short, medium and long-term outlooks, the algae blooms will be affected by the provincial nutrient management strategy. The less blooms there are, the lower the toxin levels will be and the healthier the lake.
Farm fertilizers, food processing, municipal sewage and septic tanks are considered to be the leading sources for excess nitrogen and phosphorus.
Williamson said an education campaign on soil testing for farmers has started. It's believed farmers often over-fertilize their fields because they don't know what concentrations of nutrients are already in the soil.
Excess nutrients end up in groundwater run-off and ultimately find their way into the lake.
There is also a movement to protect natural growth along the Red and Assiniboine rivers to prevent erosion and reduce run-off.
And Williamson said there have been conversations with officials in Minnesota and North Dakota about the contributions from their part of the Red River basin. It's estimated about one-third of the nutrients in the lake originate south of the border.
He said the tough thing about the lake is there isn't one large source. There are many small sources and it means many small changes have to be made to see a difference.