The Lake Manitoba

Excess nutrient loading is a common problem in drainage basins with significant human populations, and the Lake Manitoba watershed is no exception. Livestock production around the lake and inadequate cottage sewage handling are two of the most important sources. A heightened phosphorous-to-nitrogen ratio in certain areas of the lake has lead to blooms of blue-green algae, which pose a variety of threats to the aquatic ecology. Not least among them is the production of microcystin, a toxin that was present in the lake at three times the recommended maximum level in 2001.

In addition to nutrient loading, the artificial control of its water levels is perhaps the most significant detriment to Lake Manitoba's ecology. The lake's marshlands, including the Delta and Netley-Libau marshes, have been given world-class designation. However, they are not as healthy as they used to be. The Fairford dam was constructed in the mid-1950s in response to lake-wide flooding. Artificial control of water levels over the last half-century has had an impact. Stable water levels can have a dramatic effect on marsh ecology.

Marshes require both floods and droughts to thrive. During droughts, seeds grow in exposed mudflats, replenishing and renewing the marsh vegetation. During floods, plants are drowned out of deep sites, preventing overgrowth. The control of water levels since the construction of the Fairford dam has interfered with these natural processes, diminishing the extent and quality of marshlands on the lake. Scientists have also observed declines in the commercial fish populations and the muskrat population since the construction of the dam.