When rain falls or snow melts across Denver, that’s stormwater. Stormwater safely and efficiently drains through an infrastructure system operated by the City and County of Denver. The City’s stormwater system is completely separate from the sanitary sewer system. It serves a total land area of approximately 154 square miles of urbanized watershed. The City’s landform naturally directs stormwater to 67 different defined drainage basins, which flow into 20 drainageways. The entire system eventually flows to the South Platte River.

Diagram of neighborhood with sanitary sewer pipes from houses going to treatment facility, and storm drains on street going to river and stream

Denver’s stormwater conveyances include:

  • Curbs and gutter along streets
  • Almost 24,000 inlets
  • 800 miles of storm main pipes
  • More than 600 outfalls to Cherry Creek and the South Platte River

This entire system is known as a Municipal Separate Storm Sewer System (MS4). The State of Colorado issues Denver an MS4 permit, which regulates operation and sets pollutant limits.

Runoff is stormwater plus whatever it picks up as it moves across hard (impervious) surfaces of a city. Runoff can contain pollutants such as debris, trash, chemicals, soil or other substances carried by or dissolved in stormwater. Stormwater runoff in Denver’s system, like most cities’, does not receive treatment at a wastewater plant before it flows back into lakes, creeks, and, ultimately, the South Platte River.

Still, there are ways of working with nature to reduce pollutant loads. That’s why Denver has made green infrastructure a key strategy for managing the city’s stormwater. Green infrastructure refers to the use of vegetation, soils, and natural processes to decrease volume of runoff and, sometimes, actually treat stormwater. Denver encourages retrofitting of a patchwork of many, small green infrastructure installations across the City. Green infrastructure mimics nature by slowing down, spreading out, and soaking in water.

Denver’s stormwater system is impacted by actions of residents, businesses and visitors, such as littering, improper disposal of chemicals, pet waste, eroded soil and plant matter from our landscapes. Little behaviors add up to big impacts on water quality.

How do we keep stormwater clean from drain to stream? 

Help safeguard our lakes and streams!

Contact Denver 3-1-1 if you notice any of the following unusual conditions that can affect our lakes and streams:

  • A change in color of the water 
  • An unusual or foul odor 
  • Suds when there is no precipitation occurring 
  • Any unusual-looking substance discharging from a storm outlet 
  • Illegal dumping activity 
  • Soil, debris, or liquids coming from construction sites or industrial sites 
  • Large number of dead or dying fish or crayfish

Within Denver Dial: 3-1-1
Outside Denver: (720) 913-1311