UMATILLA, MORROW Counties -- A swarm of more than 100,000 mosquitoes is set to descend on Umatilla and Morrow counties, prompting vector control districts to issue warnings for residents, livestock owners and attendees of the upcoming Rock the Locks concert.
North Morrow Vector Control District Manager Greg Barron and West Umatilla Vector Control District Manager Randy Gerard on Sept. 17 called the massive hatch "an unprecedented mosquito event" and said it was "unlike anything we've seen in our careers."
"It usually isn't like this, but this is what you'd call the perfect storm -- or the worst-case scenario you could have," Barron said.
In addition to the recent hatching swarm, mosquitoes trapped south of Irrigon have tested positive for West Nile virus -- the first detection of the disease in Morrow County this year, according to Oregon public health officials.
Gerard said mosquito populations have reached levels that pose a public health threat. He warned that the entire Highway 730 corridor will be affected by the outbreak, including densely populated areas such as the city of Umatilla and McNary.
"The city will be inundated at some point," he said. "Everything along that stretch, the ports and surrounding communities, will feel the effects."
He added that many people live and work in these areas and are growing increasingly frustrated as the situation worsens.
Barron said over the past five years, the U.S. Army Corps of Engineers has begun raising the water level on Sept. 1 instead of Oct. 1, and his team has observed related changes at Lake Umatilla, which is part of the John Day pool.
This year followed the same pattern, signaling to the team that mosquito activity could begin earlier than usual -- possibly within a few weeks, depending on weather conditions.
"We looked at the forecast, and it seemed pretty favorable for mosquito production," Barron said. "I was expecting them to hatch in the last week of September, like last year. But instead, they hatched just last weekend."
According to the National Weather Service, temperatures in Morrow and Umatilla counties are expected to reach the 80s this week and continue into next week.
Mosquitoes, like all insects, are cold-blooded and cannot regulate their body temperature, which varies with their surroundings. They function best at about 80 degrees Fahrenheit, become sluggish around 60 degrees and cannot operate below 50 degrees.
However, Barron noted that the newly hatched mosquitoes are not coming from Oregon, but from across the river on the Washington side.
"Our side of the river is controlled," Barron said. "We fly over the area every 10 days to two weeks, and my team uses drones and on-the-ground monitoring to keep it covered."
He added that the mosquitoes at the Umatilla National Wildlife Refuge did not originate from McCormack Slough, but instead blew over from Paterson Slough in Benton County, Washington.
However, most of the mosquitoes have already hatched, Barron added, but there could be another wave of eggs that haven't yet come into contact with water that are triggered by favorable weather.
"I looked at the long-term forecast for our area, and it predicted warmer-than-usual weather through September, October and into November," he said. "We've had bad mosquito problems crossing the river before, but nothing like this. We've never seen it this bad."
He said everything had to line up perfectly for the outbreak: warm weather, rising water levels and eggs already laid.
The area is dense with vegetation and sits at one of the narrowest points of the river, making it easy for mosquitoes to cross. Barron said the mosquito population numbers are in the hundreds of thousands and could grow even larger.
Barron noted that they can control the current mosquito population, but if the mosquitoes across the river remain unchecked -- since those areas are not being treated with larvicide -- another hatch could occur.
"The only thing we can hope for is colder weather or the river level going down," he said.
Barron said the vector team is moving forward with plans to bring in a contingency aerial contractor, Vector Disease Control International, to help manage the outbreak.
The North Morrow Vector Control District team has been working diligently, conducting mosquito trapping and planning fogging in the Irrigon and Boardman areas to curb the growing mosquito population. Meanwhile, the West Umatilla team has also prepared to set traps on their side of the river.
Gerard said the sheer number of mosquitoes has made it nearly impossible for people to work or spend time outdoors. He noted that livestock, particularly horses, remain in a constant state of agitation.
Barron said he spoke with a rancher in Boardman on Sept. 13 who reported unusual behavior among his livestock.
"The cows were running around like crazy, and the horses were running, too," Barron said. "The mosquitoes were biting them and stressing the animals -- that's how bad it was."
Barron also said that the phone calls from concerned residents have been overwhelming.
"Yesterday, the calls didn't stop all day. I couldn't answer them all, so I posted on Facebook community pages and our website explaining the situation and apologizing that I couldn't return every call," Barron said. "Usually, I always get back to people, but this has been unbelievable."
With the upcoming Rock the Locks concert scheduled for Sept. 26-28, the West Umatilla Vector Control District is closely monitoring mosquito activity and preparing traps ahead of the festivities, Gerard said.
"We always keep a close eye on large events to ensure they aren't overwhelmed," he said. "On a daily basis, we also monitor neighborhoods to make sure they aren't being inundated."
The team is also watching to see how mosquito populations respond to changing weather patterns and how far they may travel.
The species causing concern is Aedes mosquitoes, known for being strong fliers. "They can travel miles very quickly," Gerard said.
Although vector control officials are responding as the situation unfolds, Gerard said the outbreak was unavoidable given the circumstances.
"It is pretty bad," Gerard said. "This is a unique scenario where these mosquitoes come across, and it's a very wild situation."
As a precaution amid the current mosquito outbreak, Barron stressed the importance of using repellent to stay protected.
"There are many types available," he said. "Natural options like oil of eucalyptus and peppermint can be effective. Others, like Picaridin and DEET, are also proven to work well."
He advised adults to apply repellent on themselves and their children before spending time outdoors.
"If you're worried about allergies or reactions, test the repellent on a small patch of skin first. If there's no adverse reaction, you should be good to go," Barron said.
He urged residents to stay prepared, be responsible and carry mosquito repellent given the current situation.