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West Nile virus and storm water management


A. Is a wet detention pond a breeding area for mosquitoes that carry the West Nile Virus (WNV)?

Wet detention ponds are typically designed to have a 3-foot pool of water which is not the preferred breeding area for the type of mosquitoes that carry West Nile Virus (genus Culex), referred to as container mosquitoes.

B. Why are wet detention ponds being developed?

Wet ponds are important for both flood control and water quality protection. Wet ponds temporarily hold water and release it slowly allowing sediment and other pollutants to settle to the bottom of the pond instead of being carried into lakes and streams. A DNR-recommended wet detention pond design standard is available on the Storm water post-construction technical standards page.

C. What are the primary breeding areas for mosquitoes that carry WNV?

Stagnant pockets or shallow (typically less than 3-feet deep) pools of water that exist for 7 days or more. These primary breeding areas include discarded tires, bird feeders, clogged gutters, buckets, and other areas with shallow stagnant water.

D. Should we eliminate all possible sources of mosquito breeding habitat?

It is not possible. We need to realize that mosquitoes are a part of the ecosystem. Trying to fully eradicate them would cause adverse environmental consequences, however, we can take steps to limit the habitat of the breed of mosquitoes that carry West Nile Virus. People can take steps to reduce their risk of exposure. See the Wisconsin Department of Health & Family Services: West Nile Virus

E. Are there alternative designs or treatments for stormwater instead of relying on wet detention ponds?

Yes. The problem is that areas developed into parking lots, roads and rooftops (impervious areas) lead to more runoff with less water infiltrating into the ground. This can be offset by trying to minimize the amount of impervious areas and, where feasible, direct runoff to vegetated areas that are designed to infiltrate water into the ground within a 24-hour period.

F. Can wet detention ponds become prone to mosquito breeding?

A wet detention pond is designed to fill up with sediment and other pollutants. When the permanent pool becomes too shallow, generally less than 3-feet, the property owner or other responsible party (sometimes the municipality) needs to dredge the sediment that has accumulated in the pond. If a wet detention pond becomes noticeably shallow or develops stagnant areas, then dredging should be done as the pond can then become mosquito-breeding habitat.