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It is a common misconception that stormwater is treated before reaching waterways. 

What's in the stormwater?

Stormwater contains many various types of contaminants.

  • animal feces, carcasses 
  • oil, grease, antifreeze
  • soil sediment, sand
  • pesticides, fertilizers
  • road salt
  • metals
  • etc.

The First Flush

Usually the stormwater that initially runs off an area will be more polluted than the stormwater that runs off later, after the rainfall has 'cleansed' the catchment. The initial runoff after a dry period is called the first flush. In areas with high proportions of impermeable surfaces there is a high concentration of contaminants in the runoff. 

Thermal Pollution

Many parking lots are paved with black asphalt which get warmed from the sun. Runoff from the parking lots absorb some of the heat before being quickly transported to a stormwater pond or the receiving stream. The stormwater ponds are relatively shallow and absorb heat from the sun. As a result, the temperature of the stormwater is warmer than the receiving stream and has the potential to affect sensitive fish.

Recreational Uses

Stormwater ponds and wetlands can be used for recreational purposes as long as you do not come into direct contact with the water.


Identify what the pest is. Talk to the Parks Department to help you decide the most efficient pesticide choice. Don't use pesticide if there is rain in the forecast.

Last updated: 1/3/2012 1:26:07 PM