Highs and Lows of the Rideau River
The Rideau River and its 31 locks are integral to the Rideau Canal. In their management of the Canal, Parks Canada raises the River's water level in spring. Usually 3 to 3.5 m is needed, especially in the section between Long Island and the Ottawa River, to facilitate boat traffic. In autumn the water level is lowered an equivalent amount in order to prevent flooding. This practice also prevents ice damage to the locks.
This fluctuation in water levels has an impact on the plants and animals of the River, especially native freshwater mussels and fish.
Each autumn many mussels find themselves high and dry, far from the lowered water of the River. Without water, most die within days.
Numerous fish become trapped in pockets if the water level is lowered so quickly in autumn that they do not have enough time to move out of the shallow weed beds into the main channel.  In spring, if the water level is raised too late, some fish might not make it to their spawning grounds in time. Furthermore, if the water level is raised too quickly around spawning time, eggs might be washed away with the current.
The eastern silvery minnow has disappeared from the Rideau River. This is only minnow whose eggs do not attach to underwater rocks or plants. The Project's researchers believe that the water level fluctuations have affected this species; likely their eggs were washed away.
In 1997 the lockkeepers changed their practices. Now, the water level is raised or lowered over about two weeks. Previously, the change was effected in 24 hours. The more gradual change diminishes the repurcussions for fish populations.
The water level fluctuations are of benefit to efforts to limit expansion of certain, less desireable species. When the level is decreased, the zebra mussels that are on lock walls are exposed to the air and cold. Because they are unable to survive these conditions, the practice contributes to efforts toward keeping growth of the population in check.
|Last Update: 2007-07-17|
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