Portage Diversion - Effects On Lake Manitoba

Effects On Lake Manitoba

When the Portage Diversion is opened, it sends water intended for Lake Winnipeg, a freshwater lake, into the slightly saline Lake Manitoba. This has a dramatic effect on Lake Manitoba water quality. In 2009 alone, when the Portage Diversion was open for just 27 days, the Portage Diversion itself contributed 99 percent of the suspended sediments, 60 percent of the nitrogen, and most importantly 93 percent of the phosphorus that flowed into Lake Manitoba that year. The result of the excess nutrients sent into Lake Manitoba is that eutrophication of the lake occurs. The result of eutrophication is that microorganisms such as cyanobacteria, a nitrogen fixing microbe can utilize the abudent supply of phosphorus to propagate itself. The end result is algal blooms which can result in the release of cyanotoxins in the case of cyanobacteria that are harmful to both humans, animals, and other marine life. The end result of all this leads to the deterioration of water quality, loss of aquatic life, disrutption of the ecosystem, and the real chance that the body of water could become a "dead lake" like Lake Erie in the 1960s.

The Portage Diversion has also contributed enough water at times to Lake Manitoba to cause the lake to rise significantly. The first major occurrence of this was during the 1976 flood on the Assiniboine River when 1,420,000 acre feet (1.75 km3) of water was diverted to Lake Manitoba, resulting in a 1.22 feet (0.37 m) direct rise in water levels. The flooding on Lake Manitoba in 2011 has been more severe as a result of the operation of the Portage Diversion. As of June 13, 2011 at least 3,000,000 acre feet (3.7 km3) (2.6 feet (0.79 m) rise) of water has been directed toward Lake Manitoba rather than Winnipeg and the Red River, this number already being more than double the volume of the 1976 flood. After considering the fact that without the existence of the Portage Diversion, some water would flow into Lake Manitoba near Delta Beach through oxbow lakes and channels which were at one time the original channels of the Assiniboine River when it flowed to Lake Manitoba naturally around 2000 years ago, it is estimated that the Portage Diversion contributed to about 2 feet (0.61 m) of a rise in water levels on Lake Manitoba, accounting for roughly two-thirds of the rise of the lake since the spring thaw.