The disappearance of small wetlands is increasing algal blooms says researcher Nandita Basu of the University of Waterloo.
The wetlands filter out farm runoff, she says that she and her doctoral student Frederick Cheng have found.
Blue-green algae thrive on nutrient-rich farm runoff and/or sewage from cities and towns.
On Friday, the Grand River Conservation Authority announced Conestogo Lake would be closed to swimming and fishing until futher notice. The reservoir tested positive for blue-green algae over the weekend.
"When we compare small versus large, we always compare on an equal area-basis," Basu told CBC News, "So what I mean by that is that 10 one-hectare [wetlands] is better than one 10-hectare [wetland]."
Basu said they are more effective because there is less existing water in smaller wetlands and when farm runoff makes its way to the wetland, more water is able to make contact with the soil — where the nutrient filtration happens.
Governments on both sides of the border are expecting farmers to change management to sharply reduce phosphorous runoff into Lake Erie.