Harmful algae bloom has been spotted near Colchester Harbour.

A map from the National Centres for Coastal Ocean Science shows the Western Lake Erie basin and an algae bloom stretching from Ohio to Colchester.

The discovery is the focus of work being done by researchers from Canada and the United States this week, and involves staff from the Great Lakes Institute for Environmental Research (GLIER) at the University of Windsor.

"What the satellites don't do is tell us whether the bloom is producing toxins or not and so that is going to be an important mission of (our) work," says Mike McKay, the executive director of GLIER.

Scientists have projected that this year's bloom is likely to be among the five largest since they began ranking them going back to 2002, due to heavy rains in the spring and summer.

McKay agrees.

"Since 2015, we've had I think probably the three biggest blooms on record if we include this year as well," says McKay, who was among dozens of volunteers on eight boats gathering 175 water samples from Lake Erie on Wednesday. They will be tested in the U.S. on Thursday.

Of the nine water samples taken between the mouth of the Detroit River and Colchester Harbour, none were green.

"That's a great sign," says Ken Drouillard. "It means our water intakes are protected. It means our fish are in good habitat and good health."

But McKay knows not all areas of Lake Erie will be as lucky, and that poses a great risk to the water and the economy.

"The GDP for the entire Great Lakes region is around $8-trillion Canadian annually," notes McKay, due to the shipping, fishing and tourism industries. "If the Great Lakes region were a country, we'd have the third highest GDP in the world."

One crew did find slightly green water between Colchester and Pelee Island. A third group collected green water just west of Pelee Island.

"We need to reduce phosphorus loading into the Great Lakes into Lake Erie by about 40 percent to reduce the impact of these blooms on the eco-system and our economies," says McKay. "I'd say it's arguably the most important natural resource in North America.

Algae blooms are becoming an increasing concern. They have caused water warnings and beach closings this year from Vermont to the Gulf Coast, but Lake Erie has been hit particularly hard over the past decade.

Five years ago a toxic bloom caused a two-day shutdown of Toledo's drinking water.

McKay hopes to see the results from Wednesday's session next week.