Watershed 101

No matter where you stand on the planet, you are on a watershed, a landscape feature also referred to as a catchment or drainage basin. A watershed is defined as an area of land where all the surface water drains into the same place, whether it's a creek, a stream, a river or an ocean. Therefore, all precipitation, such as rain or snow, that falls on a watershed ends up flowing to the same place.

There are two major types of watersheds, open and closed. An open watershed eventually drains into the ocean, whereas water in a closed watershed can escape only by evaporating or seeping into the earth. With the exception of some small watersheds in the Prairies and British Columbia, most watersheds in Canada are open. The rain that falls in the St. Lawrence River watershed, for example, winds up in the St. Lawrence, which flows into the Atlantic Ocean.

Watersheds have variety

Watersheds can be urban, rural, wild or anywhere in between. Toronto, for example, contains seven river watersheds, each draining into Lake Ontario, which itself is part of the Great Lakes Basin watershed. So watersheds come in all shapes and sizes and cross provincial and international boundary lines. They are populated with freshwater features such as lakes, ponds, reservoirs, groundwater aquifers, snowpacks, glaciers and icefields.

Water problems flow downstream

Because all the water in a watershed shares the same fate and flows to the same place, watersheds are sensitive to pollution and land use. Industrial pollution, agricultural runoff, erosion and logging, untreated sewers and more can affect water quality not just in one watershed but in all others downstream. Watersheds contain streams and rivers that direct water to the ocean, so what we do on land and in our waterways affects our deltas, estuaries and oceans.