Abstract: As the "sewers" of mountain landscapes, freshwater ecosystems are sensitive indicators of the effects of climate change and other human activities on mountain waters and the landscapes that they drain. Freshwaters originating in the glaciers and snowpacks of the Rocky Mountains form the "lifeblood" of human populations in western Canada. Without freshwaters, the major cities of the prairies and Pacific coast ould not have reached their current size and prosperity.

Climate warming is causing glaciers and snowpacks to shrink rapidly, and the seasonality of river flows to change. The combined effects of climate warming, increasing human withdrawals for municipal and industrial use, and impoundment for irrigation and hydroelectric power are diminishing these critical freshwater resources, and destroying the riparian areas that provide refugia for many key species of aquatic and terrestrial wildlife. Already, there are signs of serious problems on the western prairies as the result of mismanagement of mountain freshwaters.

Snowpacks and glaciers also trap volatile organic contaminants, some from as far away as Eurasia. These are transferred to freshwater food chains where they are biomagnified to surprisingly high concentrations. Climate warming may increase the releases of many chemicals stored in glaciers in the past, including DDT, dieldrin and other pesticides.

Introductions of alien fish species have also affected the integrity of lake and stream communities by extirpating native species of fish and key invertebrates, causing effects that cascade downward through the entire food chain. The native communities of several small lakes have been successfully restored, but so far proposals to restore the native fisheries of larger lakes of the Rockies have been thwarted by special interest groups. No streams have been restored from the impacts of alien species.

Protecting mountain freshwaters is critical to the sustainability of western Canada in the 21^st century. At present, neither federal nor provincial governments are adequately protecting them, and the scientific basis for management of cumulative human effects is inadequate.