WINNIPEG -- Manitoba is setting out to persuade half of Canada and a handful of northern United States to sign an agreement to save the country's "sixth great lake."

Manitoba Conservation Minister Gord Mackintosh said the high levels of pollution in Lake Winnipeg has earned it the dubious distinction of "Canada's number one water hot spot" and the world's most "threatened lake of 2013."

Lake Winnipeg is being threatened by huge algae blooms -- some so large they can be seen from space -- which feed partially off pollution that flows into the lake. Half the water going into the lake comes from Manitoba and the rest comes from other parts of Canada and the United States, Mackintosh said.

The clean water agreement would need signatures from Saskatchewan, Alberta and Ontario, as well as North Dakota, South Dakota and Minnesota, Mackintosh said.

He said it's time everyone did their part to save the 10th largest freshwater lake in the world.

"The clock is ticking. We have to get going now," Mackintosh said Thursday. "Clearly, we have got to take efforts to save our great lake to a new level."

The province is now putting together a "Lake Friendly" alliance, which will hold consultations and draft language aimed at cutting in half the pollution flowing into Lake Winnipeg. It won't be easy to convince everyone to clean up local waterways, but Mackintosh would like to see an accord signed in the next few years -- by 2020 at the latest.

"There will be negotiation. There will be a lot of effort needed," he said. "But we know that it can be done."

Manitoba has brought in restrictions on hog farming and fertilization, as well as forced Winnipeg to upgrade its sewage treatment plant in a bid to reduce the phosphorus and nitrogen flowing into Lake Winnipeg.

Still, others believe the province could do more while it tries to convince other jurisdictions to pass legislation protecting local rivers, streams and lakes. Ron Thiessen, executive director of the Canadian Parks and Wilderness Society in Manitoba, said getting a signed agreement is a good plan.

But he said Manitoba could do more in its own backyard, including banning the sale of detergents containing phosphorus and extending protection for the boreal forest, which filters out water flowing into the lake.

"I'm quite pleased with the fact that there will be a Manitoba-specific component of the initiative as well because ... we have to get our act together in Manitoba and (show) we're serious about it here," Thiessen said.

"All Manitobans need to look at themselves personally and how they can do a better job at protecting the lake."

Experts say the very health of the lake is at stake. Henry Venema, vice-president of the International Institute for Sustainable Development, said collective action is crucial.

Without having a cross-border alliance, Venema said jurisdictions don't have a way to share what practices work best. Although the lake is under serious threat, Venema said it's never too late.

"The best time to plant a tree is 100 years ago. The second best time to plant a tree is today," he said.

"You can accept the slow process of degradation or you can say at some point, we're going to start and we're going to get organized ... because we're not going to wait any longer."