The Ottawa River is one of the most highly regulated rivers in Canada, with over 50 major dams and hydro-electric generating stations scattered throughout its tributaries and mainstem. If you count all the smaller water control dams in the river system, there are hundreds of dams throughout the watershed. For example, on the Mississippi River alone there are over 30 water control structures. The Dumoine River is the only tributary in the watershed that has no constructed dams and therefore benefits from a natural flow regime. Many of the major dams have been in place since the early 1900’s, built at a time when environmental impacts were rarely questioned. A century later we are witnessing the effects these dams are having on our river system.

There are 13 principal reservoirs in the watershed, principal being defined as a reservoir with more than 200 million cubic metres of storage. These large reservoirs store a significant portion of the spring runoff and help to substantially reduce the magnitude of the second spring flood peak which typically occurs in early May. Given that the lower section of the Ottawa River is largely unregulated (there is relatively little storage provided by the many dams), the dams have limited effect on the first flood peak that we experience in the Ottawa area, which occurs about mid-April.

The dams throughout the watershed were generally constructed for one of three purposes: flood control, power generation or improved navigation. Often dams are touted as providing enhanced recreational opportunities although this can be argued both ways (enhanced if you are a power boater or sailor, made worse if you are a whitewater paddler). Many of the dams in the watershed are multi-purpose, providing some combination of flood control, power generation and recreation. The combined capacity of the hydro-electric generating stations in the watershed is over 4000 MW, producing over $1 million worth of energy on a daily basis.

The numerous dams and generating stations throughout the watershed are operated by a small handful of corporations and government agencies. Given the importance of coordinating the operation of the dams, the Ottawa River Regulation Planning Board (ORRPB) was established in 1983 by the Governments of Canada, Ontario and Quebec to ensure integrated management of the principal reservoirs in the watershed. The goal of the ORRPB is to provide protection against flooding along the Ottawa River and its tributaries, and at the same time maintain the interests of the various users, particularly the hydro-electric energy producers. The Planning Board also works to ensure that downstream communities such as Montreal have sufficient water supply at times of low flow. The ORRPB is the only inter-provincial government agency that is working in a management capacity in the watershed.

What impacts do the dams have on the Ottawa River System?

The impacts of dams on river systems are well-documented and numerous. A few good sources of information that details the research proving impacts of dams on river ecosystems are listed here:

In the Ottawa River system the dams and reservoirs create the following problems:

  • Blocking upstream and downstream migration of fish and mussels, thereby preventing them from reaching spawning and feeding areas
  • Flooding, erosion, habitat washout
  • Scouring and armoring of the riverbed by infrequent and large releases of water
  • Rapid fluctuations in flow that do not mimic the natural flow patterns in rivers
  • Modification of water-quality parameters including water temperatures, nutrient concentration and dissolved oxygen

For more detail on the impacts that some of the mainstream dams have had on fish populations in the Ottawa River System, see Tim Haxton’s report: Review of the historical and existing natural environment and resource uses on the Ottawa River.

For more detailed information about dams in the Ottawa River Watershed , check Ottawa Riverkeeper’s 2006 River Report.