Standing Water – lakes and ponds

Lakes result from either barriers to drainage or when depressions (or excavations) form along a drainage system

Majority of lakes are found in glaciated areas and are formed by glacial action

Others are formed in river channels (oxbows), by geological faulting, volcanic action, or sea level changes

Beavers form ponds by blocking drainage and then excavating the basins and seal the dam with the mud they dig up—lakes and man-made reservoirs are formed in much the same way—excavation and impoundment.

The vast majority of lakes in the world occur in glaciated areas—74%

Glacial lakes

Glaciers can form lakes in the following ways:

Ice can impound the flow in a drainage system

The flow can be blocked by glacial till or moraines

Ice flow can scour or deepen a basin

Ice blocks in till can melt out to form a “kettle” or “pothole” which then fills up with seepage or surface flow

Mountain glacier

Moraine

Moraine dams tributary stream

Glacierrecedes

Moraine

•After the mountain glacier recedes a large lake can fill the scoured out valley.

•The moraine damming the lake outflow maintains the level

Glacier recedes

Moraine at the outlet of Upper Waterton lake

A Proglacial lakeA river is blocked by ice, usually from a large continental glacier

•the water flowing toward the glacier forms a large lake at the glacier margin

•Following the retreat of the lastglaciation most of the Canadian landscapewas covered by proglacial lakes•Species tolerant of coldwater (salmonid and coregonids) became very widespread. •Opportunities for dispersal of cool and warmwater species were much more limitedbecause these water bodies disappeared with the ice.

Proglacial lakes

Probable Waterton glacial lake at the height of the Wisconsin glaciation>12,000 yr bp.

This lake would have been fed by the all of the tributaries of the Oldman system

western extent of the continental glacier

Eastern extent of the cordilleran glaciers

Present Waterton lakes

This lake probably served as a major refugium from which fish and invertebrates colonized the SSRB, after the ice age.

Genetic studies indicate that many lake trout populations across western Canada came from this glacial refugium

Proglacial lakes in southwestern Alberta and Montana (around 12,000 Bp)

Waterton Lakes have a similar origin—Both Waterton and Memphremagog have contain glacial relict animal species in their deep waters.

Freshwater mysid shrimp are important glacial relicts and have a restricted range because of this.

They have been introduced to many lakes because fisheries managers thought that this would improve fisheries yields

This has largely backfired because Mysis tends to compete with epilimnetic zooplanktivorous fish, and because of their vertical migrations are difficult for these fish to consume.

Most of the mysids for the introductions to other western lakes came from Upper Waterton Lake