I step onto the muddy bank of the Bow River on an early July morning, my rubber boots sinking into soil that hasn’t been this saturated in decades. The air buzzes—literally—with activity. What would normally be a peaceful morning walk has become an exercise in constant swatting and slapping.
“I’ve lived in Calgary for 32 years and I’ve never seen anything like this,” says Martha Weins, a retired nurse who meets me at Prince’s Island Park for our interview. Her arms bear the telltale red welts of recent mosquito encounters despite being covered in repellent. “It’s like they’re coming in waves.”
She’s not wrong. Calgary is experiencing a mosquito population explosion following the wettest spring on record, with May rainfall nearly triple the historical average. Those puddles and standing water have created perfect breeding conditions for mosquitoes—including those that can carry West Nile virus.
City data shows mosquito trap counts are up 240% compared to this time last year. More concerning, the proportion of Culex tarsalis—the species that transmits West Nile virus—has increased dramatically, now representing about 18% of mosquitoes trapped, compared to the typical 5-8%.
Alberta Health Services confirmed the first positive mosquito pool for West Nile virus in Calgary’s northeast last week, the earliest seasonal detection in over a decade.
“The combination of early heat and abundant standing water has accelerated mosquito reproduction cycles,” explains Dr. Samia Rahman, an infectious disease specialist with the University of Calgary. “We’re seeing multiple generations of mosquitoes emerge much faster than our typical pattern.”
The Bow and Elbow Rivers, which weave through Calgary’s urban landscape, have expanded their floodplains after weeks of heavy rain, creating countless breeding habitats. Behind homes in riverside communities like Bowness and Inglewood, formerly dry ravines now harbor stagnant water where mosquito larvae develop.
For most Calgarians, the surge is merely an annoyance—forcing changes to outdoor plans and sending families scrambling for bug spray that’s increasingly hard to find on store shelves. But health officials warn the risk goes beyond itchy welts.
“West Nile virus isn’t just a theoretical risk,” Dr. Rahman tells me. “While about 80% of people infected show no symptoms, those who develop West Nile fever experience flu-like symptoms that can be debilitating for weeks. And for about one in 150 infected people, the virus causes neurological complications that can be life-threatening.”
Last year, Alberta recorded just three human cases of West Nile virus. This season, with ideal conditions for both mosquitoes and viral transmission, public health officials are bracing for potentially dozens.
The City of Calgary has doubled its mosquito control program, deploying additional teams to treat standing water with Bacillus thuringiensis israelensis (Bti), a naturally occurring bacteria that targets mosquito larvae while remaining harmless to other wildlife, pets and humans.
“We’ve mapped over 200 new breeding sites since May,” says Theo Martinez, supervisor of Calgary’s mosquito control program. He shows me a tablet with a map dotted with red pins representing treatment areas. “Our challenge is that we can’t treat them all—private properties, naturally occurring water bodies in parks—the scale is overwhelming this year.”
As we talk, Martinez demonstrates how his team applies the granular Bti treatment in a partially flooded drainage ditch near the river. The work is methodical but feels insufficient against the scale of the problem. Standing water stretches in every direction beyond the park’s boundaries.
For Calgary’s outdoor workers, the mosquito surge presents an occupational hazard. Landscapers, construction workers, and city employees find themselves working through clouds of the biting insects.
“I’ve had to modify my workday,” explains Jaime Carson, a landscape architect working on several public projects. “I’m starting at dawn when it’s cooler and the mosquitoes are less active, taking a break midday when they’re worst, then finishing in the evening.”
Dr. Colin Russell, a veterinarian at McKnight Veterinary Hospital, reports seeing a 60% increase in visits related to mosquito-borne health concerns in pets.
“We’re seeing dermatitis from excessive biting in dogs, and more concerning, we’ve had two confirmed cases of heartworm this season—something rarely seen in Calgary,” Dr. Russell explains. “Mosquitoes transmit heartworm larvae, and with climate change extending our mosquito season, diseases we used to consider ‘southern problems’ are moving north.”
Historically, Calgary’s location at over 1,000 meters elevation with typically dry conditions has protected it from the mosquito populations seen in more humid parts of Canada. Climate researchers suggest that advantage is eroding.
“What we’re witnessing aligns with climate change projections for southern Alberta,” says Dr. Manisha Kulkarni, a medical entomologist with the University of Ottawa who studies vector-borne diseases. “Models predict more intense precipitation events followed by periods of extreme heat—exactly the conditions that favor mosquito reproduction and accelerate the West Nile virus replication cycle within the mosquito.”
Back at Prince’s Island Park, city workers are posting new warning signs about mosquito activity and West Nile risk. The bright yellow notifications seem strangely clinical against the lush green background of the park. Nearby, a family abandons their picnic after just minutes, defeated by the constant assault of hungry insects.
Alberta Health Services recommends wearing long, light-colored clothing, using DEET or icaridin-based repellents, and eliminating standing water on properties. They also suggest avoiding outdoor activities at dawn and dusk when mosquitoes are most active.
For Martha Weins, the retired nurse I spoke with, these precautions have become second nature this summer. “I’ve lived through Calgary floods, windstorms, and hail the size of golf balls,” she says, swatting away another mosquito. “But sometimes it’s the smallest things that change how you live. I’ve had West Nile before—got it in 2017. Took me almost three months to feel normal again. I’m not risking that twice.”
As climate patterns continue to shift, this summer’s mosquito surge may represent not an anomaly but a preview of Calgary’s future—one where residents must adapt to new biological realities in a city built for different conditions.
