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Wet and Dry Stormwater Ponds

A pond is a type of stormwater management facility designed to collect rainwater and pollutants and prevent downstream flooding.

  • Wet ponds always have a pool of water.

  • Dry ponds only have water after rain.

Image of a stormwater pond.Ponds have an embankment (called a dam) to hold back water that is entering the pond. Most dams are earthen (not concrete) and are grass covered. All stormwater ponds also have a control structure that releases water at a much slower rate than the stormwater entering the pond. While water remains in the pond, pollutants have time to settle at the bottom.

Most ponds located throughout Montgomery County are stormwater management ponds, even ones that are community amenities. Ponds can have many different designs, including ponds with concrete channels, dry ponds with sand filters on the pond bottom, and ponds that provided wetland habitat around the edges.

 

Why are Stormwater Ponds Important?

Stormwater ponds are important stormwater management tools, because they:

  • Remove pollutants 

  • Improve health of streams and rivers

  • Help to make our waters fishable and swimmable

  • Improve the quality of the Chesapeake Bay 

As rainwater flows over hard surfaces and lawns it picks up pollutants such as sediment, trash, pesticides from lawns, nutrients from fertilizer or pet waste, and oil and grease from cars. Ponds can help to reduce this pollution from entering our waterways.

Image of a dry pond with a sand filter.
A dry pond with a sand filter on the bottom. 

 

Maintaining Stormwater Ponds

As the property owner, you are responsible for all maintenance of your stormwater pond unless a shared maintenance agreement has been made with the DEP Stormwater Facility Maintenance Program.  Ponds at County facilities and schools are the maintenance responsibility of the Department of Environmental Protection. 

Stormwater ponds require regular maintenance similar to other landscaped areas, including grass cutting, trash removal, and vegetation management. Please visit the stormwater facilities maintenance page for a list of approved contractors. DEP-approved contractors are recommended but not required for non-structural maintenance. 

Graphic of a pond and suggested location for performing maintenance.Un-maintained ponds may:

  • Not remove pollutants as intended, sending polluted water to streams and rivers

  • Become filled with sediment and debris, so water cannot be stored in the facility, which may lead to downstream flooding and erosion

  • Look unsightly with excessive growth of unwanted weeds or algae

  • Cost more to fix problems if left unchecked

  • Lead to a dam breach if overgrown vegetation and trees compromise the pond safety over time. This would cause flooding and damage to surrounding properties and adjacent homes

  • Have inlet and outlet areas blocked by excessive growth or debris. This will cause water to back up or pond on adjacent properties

By maintaining your stormwater pond, you are doing your part to help the environment and protect your local streams and the Chesapeake Bay.

 

How Will I Know What Maintenance is Required?

Montgomery County regulations require that you perform ongoing routine grass cutting, trash removal, and vegetation management of your stormwater facility. If the work described below is not done regularly, you could receive a notice of violation.

Grass Cutting

✔ Mow grass in the pond area at least twice a year

  • Downstream slope of dam
  • Top of the dam
  • Upstream slope of dam (dry pond only)
  • 25 feet around the control structure (dry pond only)
  • Inlet channels, around headwalls, and pipes within pond area (where safe and accessible)
  • Outlet channel

 

Image of the front of the Non-structural Pond Maintenance Fact Sheet.
Need Help with Basic Pond Maintenance and Troubleshooting?
Download the Fact Sheet
(PDF, 1.54MB)

Vegetation Management

✔ Manually remove all trees and woody vegetation in the following pond areas at least twice a year

  • From the top and upstream and downstream slopes of the dam
  • From inlet and outlet channels
  • Within 25 feet of the control structure
  • From channels, headwalls, and pipes into the pond area

 Do not apply herbicides, fertilizers, or pesticides in or around the pond. If  manual removal of invasive weeds has been ineffective, limited applications of aquatic friendly herbicide may be applied by a qualified professional certified by the State of Maryland.

The most commonly forgotten non-structural maintenance is mowing and removal of trees and woody vegetation on the downstream slope of the embankment.

 

Trash Removal

✔ Remove trash and debris from all areas in and around the pond monthly

  • For wet ponds, any trash in the water should be removed safely by professionals

 

Image of the front of the Structural Pond Maintenance Fact Sheet.
Want Help with Pond Structural Maintenance?
Download the Fact Sheet
(PDF, 1.07MB)

Other Preventive Maintenance

As needed

✔ Know the pollutant sources on your property and try to reduce or eliminate the pollutants at the source

✔ Notify DEP if beaver activity or animal burrowing is observed 

✔ Prevent trees and woody vegetation from growing in these areas

✔ Seed and cover adjacent areas of bare soil to prevent erosion

✔ Notify Montgomery County police if graffiti is observed 

✔ Verify all pond safety signs are in place 

✔ Inspect the facility after every major storm and contact DEP if you are concerned

These basic actions will keep your facility working correctly and prevent more serious repairs, which will save you ​money in the long term. 

 

 

 

Structural Maintenance

Structural maintenance must be performed by contractors who have been approved by DEP. No one should remove control structure manholes or enter the control structure without proper training, certification, and permits for confined space entry. Entering the water or any confined spaces without these requirements is a violation of State law and could be dangerous or deadly.

Structural Maintenance Issues
  • Missing pond safety sign  
  • Shoreline erosion on the dam embankment
  • Leaking control structures and pipe joints
  • Accumulation of sediment and debris within the ponds
  • Dry pond holding water longer than 72 hours
  • Cracks or damage to the concrete control structure
  • Damaged or corroded trash racks
  • Damaged or clogged inlet and outlet channels, pipes, and trash racks

 

 

Serious Failures
(Require immediate attention! Notify DEP As Soon As Possible)
  • Cracks or sink holes on the dam embankment
  • Damaged or broken control structure
  • Slope failure on the dam embankment
  • Beaver lodges in the wet pool blocking outlet pipes
  • Animal burrows in the dam embankment
  • Missing manhole covers on the control structure

 

Ponds in the Stormwater Facilities Maintenance Program

Image of a man mowing around a stormwater pond.The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transferred their maintenance to the County. The program also maintains facilities that were required as part of the Department of Planning permits.

Not sure if your stormwater pond is part of the Stormwater Facilities Maintenance Program?  Check out online Facilities Map or email askdep@montgomerycountymd.gov.

 

Can I remove my stormwater pond after installation?

No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of these facility locations as part of the Stormwater Facility Maintenance Program. DEP may perform a maintenance inspection of your practice if it is a permitted structure.  Property owners must contact DEP before any major changes can be performed to the structure. 

 

 

Pond Safety and Concerns

Mosquitoes

Stormwater ponds that are functioning as they were designed should not cause mosquito problems. DEP has developed a webpage and brochure with all the information you need to identify if mosquitoes are coming from a mal-functioning stormwater management facility and how to prevent these issues. The webpage also contains general information on mosquito biology and prevention.

Visit the DEP Mosquitoes webpage

 

Pond Signage

The Montgomery County Code (section 36-3) requires that a person who owns or controls land that includes a publicly accessible pond must post warning signs around the pond and at any major approach to the pond, such as a path. A publicly accessible pond is defined as a water impoundment that:

  • Retains a permanent pool more than 24 inches deep and 20 feet across at its widest point

  • Is not a swimming pool as defined in Chapter 51 of the Montgomery County Code

  • Is not surrounded by a continuous, permanent fence or barrier (at least 4 feet high with no opening wider than 2 inches) within 100 feet of the shoreline

The County Code has established standards for warning signs, including the size, message, construction, placement, and maintenance. They are listed in the table below.

 

Standards for Pond Safety/ Warning Signs
Issue Standards
Placement
  • Warning signs must be posted on all sides of a publicly accessible pond and at any major approach to the pond, such as a path.

  • Warning signs may be posted in the pond or on the shore.

  • Warning signs must be visible from the shore and not obscured by vegetation or other obstructions.

  • Warning signs at golf courses may be posted at the main entrance to the golf course rather than at each pond.

Size
  • Warning signs must be at least 18 inches high by 24 inches wide.

  • The lettering on warning signs must be at least 2 inches high, and any graphics must be large enough to be clearly seen.

Construction
  • Warning signs must be made of a weather-resistant material such as metal, pressure-treated wood, plastic, or an approved equivalent.

  • All lettering, graphics, and the surface of the sign must be composed of a weather-resistant material.

  • The sign must be securely anchored.

Message
  • The warning sign must, at a minimum, warn that entering the water to swim, skate, or boat is unsafe. The sign may use the international symbols for prohibited activities.

  • The sign must provide a legible written message and appropriate graphics.

Maintenance
  • Warning signs required under Chapter 36 must be maintained in good condition by the person who owns or controls land that includes a publicly accessible pond.

 

Resources and Financial Incentives

Have a stormwater pond on your property? Financial incentives are available for you.

 

The Water Quality Protection Charge Credit Program

After you have installed your stormwater pond, you are now eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill).  The credit provides an incentive for maintaining your stormwater pond and other stormwater management practices.

You must apply for the WQPC credit separately – the credit will not be provided to you automatically.

Residential property owners can receive up to 50% off their WQPC depending on the type and size of stormwater management practices on the property.

Non-residential and multi-family properties can receive up to 50-60% off their WQPC depending on the type and size of the stormwater management practices on the property.

Learn more on the WQPC Credit webpage.

Image of a pond.