Dams and diversions normally go together: water is stored behind a dam, then withdrawn from its natural course for transfer elsewhere in the same or to another drainage basin.

For many years, engineering projects to redistribute river flows in favour of regions experiencing greater demand for water and electricity took the form of diversions of flow through channel modifications, canals, pipelines or similar means. More recently, entrepreneurs have also proposed to move water in bulk by ship and truck tankers, but little activity by this means has been recorded to date.

Interbasin diversion projects are found in almost all provinces, and the total flow of water diverted currently between drainage basins is enormous—approximately 4500 cubic metres per second. No other country diverts nearly as much water, or concentrates so much flow for a single function—hydroelectric power generation. Some of the largest projects being; the La Grande (James Bay) program in Quebec, the Churchill-Nelson diversion in Manitoba, and the Churchill Falls project in Labrador, all publicly administered hydroelectric power programs. The national pattern of interbasin diversions has hardly changed in the past decade.

Many of the issues with water diversions are similar to those wide-ranging and long-term biophysical and socio-economic costs associated with dams. However, other issues related to diversions and other removals of water have been experienced. Unlike dams, which in most cases block fish passage, interbasin diversions risk transferring undesirable fish and associated parasites, bacteria and viruses in the water from one drainage basin or distant source into another basin incapable of resisting them.

Another issue relates to the contribution of freshwater outflows to the marine environment. The flush of spring meltwaters from inland induces upwelling of deep, nutrient-rich salt water into the surface layer, at a time when this is most useful to marine life. Dam and diversion projects are already reducing the natural spring freshet from many rivers, with some evidence of adverse effects in terms of sediment and nutrient losses and reduced fish populations important to coastal ecosystems

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Interbasin diversions of water are widespread in Canada, but none leads south of the border. Likewise, the first ship carrying Canadian water in bulk for sale to any foreign market has yet to leave port. This is not for lack of trying on the part of entrepreneurs who continue to lobby federal and provincial governments for approval of their plans.

Read more about Water Exports and Water: How we share it?

Adapted from the National Water Research Institute's report Threats to Water Availability in Canada - A Perspective