Stormwater Management

Stormwater management facilities are often blamed for large numbers of mosquitoes, because the facilities contain rainfall runoff. But when a stormwater management facility is designed and maintained properly, it should not contribute to excessive mosquito populations. 


What are Stormwater Management Facilities?

Per State of Maryland requirements, the Montgomery County Department of Environmental Protection regulates the management of stormwater facilities to prevent stormwater pollution in our waterways.

Stormwater management facilities are landscapes or structures that are used to remove pollutants, prevent stream damage and erosion, and prevent flooding. They include large scale infrastructure projects such as roadside rain gardens, retention ponds and underground stormwater storage, As well as homeowner installed RainScapes (such as rain gardens or rain barrels).


Pond at a HOA complex A Stormwater Management Pond


Stormwater facilities have several functions:

  • They slow, collect and store or absorb stormwater runoff from urban surfaces such as roads, parking lots, and rooftops.
  • They remove contaminants from the runoff, cleaning it before it is allowed to discharge into local streams. This helps to safeguard our waterways. They are vital infrastructure in the urban environment.

There are thousands of stormwater management facilities in the County. Some of these facilities hold water permanently, while others hold stormwater temporarily.

If designed and maintained properly, stormwater management facilities should not support excessive mosquito populations because they:

  • Drain water within a week or less;
  • Contain moving water; or
  • Contain predators that feed on mosquitoes (or mosquito predators)


A bioretention garden draining 24-hours after a storm This bioretention garden drains water within 24-hours. Most will drain in two to three days





I think the nearby stormwater management facility is the source of mosquitoes in my area.  What should I do?

Although most mosquito issues on properties are not connected to stormwater management facilities, there may be occasions where the facilities are not functioning properly. 
  1. Most mosquito issues originate from small amounts of standing water in containers, potted plants, tarps, etc.  The first step to reducing most mosquito issues is eliminating those sources of standing water. Sometimes trash left near stormwater facilities might be the source of the mosquitoes. 
  2. If after checking and removing other potential mosquito sources, you still see large numbers of mosquitoes around a stormwater management facility, navigate to the the  Montgomery County Stormwater Facilities Locator page and enter your address.  Look for any green or red dots that represent a stormwater facility near your home. 
  3. Write down the "Asset Number" - the number of the stormwater facility so that County staff can easily find your facility and direct you quickly towards the appropriate person. 
  4. File a complaint through MC311. Please let the 311 Operator know the number(s) associated with the stormwater feature(s) if you have identified any near your home.