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DENVER (KDVR) — The recent wet weather has Denver bracing for a potential surge in mosquitoes. 

“It just depends on how the weather plays out over the next couple of weeks and even the next month,” said Alan Polonsky, an environmental analyst with the Denver Department of Public Health and Environment.

Polonsky and his team are monitoring about 70 sites across the city each week to check for the presence of mosquito larvae. The sites are in areas known to have large amounts of standing water.

“We use this dipper. We call it a dipper. And we put it in the water and we look for larva mosquitoes and if we get a certain amount of them in each dip, we’ll apply larvicide,” he said.

According to Polonsky, DDPHE would be doing the same testing regardless of how much moisture Denver has had this month. However, he said the rain has the potential to support a boom in the mosquito population.

“It’s definitely gotten our attention. We’ve got some habitats that we know could be a potential real problem if we’re not ready to go as soon as mosquitoes are getting more active,” he said. 

West Nile virus raises concerns

Mosquitos that lay their eggs in mud are known for reproducing in very large quantities. While they are a nuisance, DDPHE is not as concerned about them as they are about mosquitos that lay their eggs in standing water. They are the ones responsible for carrying West Nile virus. 

“Those are the ones that it’s really important to empty your wheelbarrows, empty your containers on your property,” Polonsky said. “If the water is flowing it’s not a problem. So if you get a lot of rain, you have flowing water. It’s when the water stops that you have to really be paying attention.”

According to the Centers for Disease Control and Prevention, Colorado led the nation last year with 204 cases and 18 deaths from West Nile virus. In 2021, Colorado had the second most cases of any state. Both of those years were considered dry seasons. 

“We can have higher West Nile during dry years as well,” Polonsky said. “With drought, you have maybe some more isolated water bodies that can create good habitat for mosquitoes.”

How to keep mosquitoes away

Still, he said eliminating standing water is the key to reducing the risk of exposure to the virus. Homeowners should dump out anything that collects water — like empty flower pots, wheelbarrows and tires — once per week. Standing water can also collect in gutters. 

“For the long term, I would encourage you to think about how you landscape and try and get your irrigation or your yard set up so you don’t need irrigation along sidewalks and streets,” Polonsky said. 

Denver is not the only city that may be impacted by elevated populations of mosquitoes. On the Western Slope, the Grand Valley Mosquito Control District said it expects an unusually large number of insects because of the above-average snowpack.