Two kinds of detention ponds are used in Everett, wet detention ponds and dry detention ponds.

Wet detention ponds contain water at all times and are used to treat stormwater runoff and prevent flooding during severe storms. Plants in the wet detention pond use nutients found in some pollutants to fuel growth, so fewer of these pollutants enter the natural waterways. Insects and micro-organisms living in the mud also help remove pollutants from the stormwater.

Dry detention ponds only hold water during rainstorms and their primary function is flood prevention.

Detention ponds located in multi-family complexes and condominium complexes are privately owned and maintained. Businesses are often required to build and maintain detention ponds on their business sites.City employees inspect the ponds to make sure they are functioning properly. In most single family areas the City owns and maintains the detention ponds. 

City owned ponds are tested each year for mosquito larvae (eggs). The ponds are tested about every 30 days throughout the spring and summer months begining in May. Ponds that are found to have elevated levels of mosquito larvae are treated with larvicide to reduce the mosquito population.

Privately owned ponds may be treated by the property owner at their discretion. The City does not treat these ponds.

You can learn more about mosquitoes and West Nile Virus from the Washington State Department of Health.