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Rideau Canal National Historic Site of Canada

Dead Fish in the Rideau Canal

The dead fish we commonly see in the canal in downtown Ottawa every spring is part of a normal phenomenon that occurs annually.

Parks Canada has been consulting with Dr. S. Cooke (Carleton University) over the last several years about this very issue.  Parks Canada has learned that is it very difficult to identify the exact cause of death in the fish but that it is likely that they have died of natural events such as winterkill, significant changes in water temperatures, and individual health of the fish.

This section of the Canal has a very large population of fish.   One of the most likely causes of their death is winterkill.  This phenomenon is common in lakes during the winter.  As ice forms on the surface of the lake, it acts as a cap.  Once in place, the ice limits the amount of oxygen in the water of the lake.  During the winter fish use up oxygen.  The strongest of the fish survive while those that are weaker die and sink to the bottom of the lake.  When spring arrives, the lake refreshes itself (we often hear fishermen refer to this as the Lake turning itself up-side down).  When this happens, the dead fish surface.  Water flow and wind will move the fish through the system once they have surfaced.

As part of the maintenance of the Rideau Canal, Parks Canada has a crew that travels by boat and removes the dead fish, garbage and floating mats of vegetation from the surface waters in downtown Ottawa. Parks Canada will continue this process throughout the summer as needed.