The Shellmouth Reservoir, also known as Lake of the Prairies, has seen low levels and, in a more concerning development, a fish kill as a result. Steve Topping, Executive Director, Infrastructure and Operations Division, Manitoba Water Stewardship, recently spoke with The News Review about what caused the problem in the first place.
The issue starts with heavy snow which accumulated over the winter, explains Topping. The large snow pack meant that it was anticipated the reservoir would need to capture a significant portion of the runoff, as it is one of the main flood control mechanisms on the Assiniboine river. In anticipation of the heavy runoff, the reservoir was lowered to levels previously seen in 2011.
The difference between this year and that, Topping says, is that the spring melt itself was late, which meant that the reservoir was lower for a longer period of time. This meant that water and fish were trapped in depressional areas in the bottom of the reservoir. That late melt caused low oxygen levels in these areas, which has caused a higher fish mortality rate. The other problem is that ice limits the amount of photosynthesis that can happen in these areas, further reducing the amount of oxygen.
"When you go late in the year, with no runoff coming into these depressional areas, you get low oxygen levels, because of no refreshing of the water in the areas and due to no photosynthesis occurring," Topping explains.
The late runoff means that the reservoir is about two to three feet lower than they would like it to be since it still has to meet the water needs downstream, but without the inflow necessary to maintain those levels.
Topping says that the main reservoir is still in place, and the fish there should be able to weather the poor conditions which caused the kill. He notes that this is not the first time this has happened in the lake, and in those years it quickly recovered, without much impact to the overall fish population. He notes that in 1997 there was a fish kill for the same reasons, and that did not substantially affect the fishery.
"The fishery after that event was very good. We had seen no particular class of fish that were impacted due to that fish kill in 1997. We believe the fish are healthy in the reservoir itself, but the ones in the depressional areas will have a mortality rate there."
The warm weather means that the reservoir has begun to climb as needed, and Topping says that as the snow melts on the prairies the reservoir will again be at normal levels very soon.
