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Lake Simcoe Region Conservation Authority

Lake Simcoe Region Conservation Authority > Watershed Health > Stormwater
​​​​A photo of an SUV driving on a wet road. Water is splashing away from the vehicle.

Stormwater

Stormwater is a relatively simple concept; it refers to precipitation (rainwater, melting snow) that accumulates after a storm.

Stormwater runoff, the result of what happens to stormwater once it hits the ground, particularly when it falls on paved and other hardened surfaces, is a significant environmental concern.

Stormwater runoff in natural areas is generally of minor environmental consequence. In natural areas, stormwater runoff soaks relatively quickly and easily into the ground, is absorbed by trees and plants and evaporates into the air. A small amount runs along the ground and ends up going directly in streams, rivers and the lake. 

The same is not true in urban areas. Hardened surfaces do not let stormwater runoff seep into the ground, so instead it travels over roofs, roads, parking lots, as well as lawns. The stormwater picks up pollutants like dirt, oil, heavy metals, bacteria, fertilizer, grass-clippings, pet waste, litter etc. and carries substantially more polluted runoff to our rivers and waterways.

A picture of a flooded road in Aurora. Cars can be seen floating in the water. The road is blocked by a firetruck. After heavy rains or snow melts, river levels can rise and cause flooding. Even in areas not necessaril​y prone to flooding, high intensity storms can result in localized flooding because the water can’t get into the ground fast enough. 

While both rural and urban stormwater runoff eventually ends up in our streams, rivers, and ultimately Lake Simcoe, urban stormwater is more problematic, not only because of the much larger volumes of runoff, but because of the pollutants captured and then carried in that runoff.​

An illustration showing the infiltration of water in a natural environment compared to an urban environment. Urban environments contribute to higher amounts of runoff.

​​Illustration courtesy of the City of Philadelphia

Stormwater man​agement is the practice of addressing stormwater runoff.​