As the temperatures rise and the sun lingers longer in the sky, Boulder residents are enjoying hikes, picnics, and time at local lakes. But with summer’s beauty comes an invisible buzz—mosquito season. And with it, a very real threat: West Nile virus.

While Boulder’s mountain air might feel like a natural shield, mosquitoes carrying West Nile virus have been detected in Boulder County in past years. Being informed and taking smart precautions can help keep your summer safe and bite-free.

Understanding the Risk in Boulder

West Nile virus is primarily spread through the bite of an infected mosquito. While not every mosquito is a carrier, Boulder County has had positive mosquito samples in recent summers—particularly in low-lying and wetland areas. With changing climate patterns and above-average spring precipitation, the risk tends to spike from late June through early September.

Health officials track “vector zones” where mosquitoes that carry West Nile are most active. In Boulder, these include:

• Coot Lake and Boulder Reservoir

• Wonderland Lake Wetlands

• South Boulder Creek corridor

• East Boulder’s Valmont and irrigation ditches

These areas can become mosquito breeding grounds, especially after heavy rain or irrigation runoff.

Wonderland Lake

Where and When to Be Most Cautious

Mosquitoes are most active during dawn and dusk, so any early morning jog or evening paddle around these water-rich areas increases your exposure. Hikers and dog walkers should take extra care when passing shaded trails near water.

Even high-elevation locations like Flagstaff Mountain or the Chautauqua area aren’t immune. Mosquitoes can travel farther than you think—sometimes up to several miles from where they hatched.

If you’re heading outdoors, it’s smart to stay up to date on local conditions, mosquito activity, and trail alerts by checking community wellness updates like this one.

Lost Gulch Overlook, Flagstaff Mountain

Smart Ways to Protect Yourself

Here’s how Boulder locals can stay safe without sacrificing summer fun:

• Use EPA-approved repellents, especially those with DEET, picaridin, or oil of lemon eucalyptus (a natural alternative).

• Wear long sleeves and pants when hiking or near water, particularly during early morning or evening hours.

• Drain standing water around your home. Empty birdbaths, flowerpot trays, and buckets regularly.

• Install and maintain window and door screens to keep mosquitoes out of your home.

• Avoid wearing heavily scented lotions or perfumes outdoors—mosquitoes love sweet smells.

Don’t Fall for These Myths

Citronella candles may smell nice, but they are not enough to protect you from bites. Mosquito “bracelets” and essential oil diffusers offer limited protection at best.

Also, don’t rely on elevation alone to shield you. Even at higher altitudes, mosquitoes have been known to breed in small puddles, tree holes, and stream edges.

Recognizing Symptoms of West Nile

Roughly 4 out of 5 people infected with West Nile virus show no symptoms. But for those who do, signs can include:

• Fever

• Headache or body aches

• Fatigue

• Nausea

• In rare cases, neurological complications, such as meningitis or encephalitis

If you or someone you know experiences flu-like symptoms after a mosquito bite, consult a healthcare provider immediately.

You can monitor mosquito testing results and updates through Boulder County Mosquito Control, which posts maps of high-risk zones and weekly activity updates. Additional prevention guidance is available from the CDC’s West Nile resource page.

A Safe Summer Starts with Smart Habits

Boulder’s stunning open spaces are meant to be enjoyed—but doing so safely means understanding the risks that come with the season. With a little planning and the right precautions, you can soak up all the sunshine Boulder has to offer—without getting stung by summer’s smallest threat.

Stay smart, stay covered, and make the most of your Colorado summer.

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