A two-pool wetpond.

Good: Well-maintained wetpond


A wetpond, or wetpool, is an open basin that has a pool of water year-round. The volume of the wetpond allows sediment to settle out as stormwater runs in. Wetland vegetation is typically planted to provide additional treatment by removing nutrients such as phosphorus and nitrogen.

Typically, there are two pools. Stormwater flows into the first pool, where sediment settles before moving into the second pool. The water is then discharged to streams and groundwater.

Wetponds also have additional temporary storage above the permanent water level to detain and slowly release stormwater. They often are fenced for safety and sometimes incorprate a detention pond


Virtual tour

Click on the image below to get inside of a wetpond and learn about common components and maintenance tasks.

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Maintenance needs commonly associated with wetponds

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Inlets and outlets

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Control structure

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Catch basin



Maintenance sheet


Maintenance is needed if you see these signs  

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Problem: The detention pond above is over-
grown with vegetation. 

Bare, exposed soil
Slopes that are deteriorating
Sediment that restricts flow or clogs inlet and outlet pipes
Sediment buildup, especially on base of pond
Unhealthy or dead vegetation
Blackberries or other problem weeds
Overgrown vegetation
Holes in berms or slopes
Leaves, trash and other debris
Water surface is discolored or has an oil sheen
First cell/pond is empty and doesn't hold water
Berm dividing cells should be level so water flows evenly over entire length of berm
Trees, often alders, growing on the slopes



Tips for fixing problems and general maintenance

Completely remove weeds such as blackberries and English ivy, then check for them on a regular basis and remove new vines.  Contact Clark County Vegetation Management for questions about controlling weeds at (360) 397-6140 or email vegetation.management@clark.wa.gov 

Remove cattails before they start to dominate a facility.

Remove all unplanned trees or saplings that block parts of the facility or hinder maintenance.

Make sure banks, slopes and areas designed for vegetation are planted with native or easy-to maintain species. Avoid trees near the pond and on berms.

Plant at appropriate times during the year so vegetation can get established.

Replace vegetation damaged or removed during maintenance.

Check access roads and fencing, if the facility has them. They should be free of overgrown vegetation and other materials so that the facility is easily accessible for maintenance.

Control erosion by reseeding areas where soil is exposed, especially on slopes around a facility.

Fill in eroded areas and cover them with sod, mulch or other erosion control materials.

Removing sediment is best done in July and August before winter rains set in.

Pick up leaves before rains begin.

Inspect and remove debris regularly, particularly after storms.

Remove any material clogging drains, outfalls and channels.

Avoid using fertilizers, herbicides or pesticides in or near the facility. Chemicals pollute the water and can cause unwanted plant growth.

Identify sources of leaks or spills and contain them as quickly as possible.

Check inlets and any open or confined standing water for mosquito larvae (see photos below). If mosquitoes are a concern, contact Clark County Mosquito Control District for information. The 24-hour service request line is (360) 397-8430.

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Check roads and fencing in the facility. They should be maintained to allow easy access.