Today's Mosquito Risk in Oregon: Real-Time Forecast & Activity Map
Check your ZIP code for local mosquito activity, West Nile risk, and prevention insights.
Built from CDC and NOAA data
Mosquito Surveillance Insights
- Annual WNV Cases
- about 5 to 15 confirmed cases annually
- Based on CDC ArboNET surveillance data
- Risk Tier
- Tier 4: Low
- Eastern Oregon irrigated agriculture drives WNV; western valleys see modest Culex pressure each summer.
- Per mosquito-risk-model regional tier
- Highest-Risk Areas
- Umatilla, Morrow, Malheur, Klamath (eastern irrigation belt)
Current Situation in Oregon
Oregon carries a low WNV burden of roughly 5 to 15 confirmed human cases annually, with risk concentrated east of the Cascade Range across the Columbia Basin and the eastern Oregon high desert irrigation belt. The state splits into two mosquito climates: the wet, marine Willamette Valley and the Coast Range stay cool and dry through midsummer with modest Cx. pipiens pressure, and the arid east runs hot and irrigated, with the Columbia Basin around Hermiston, the Klamath Basin, and the Malheur and Snake River corridors sustaining Cx. tarsalis through summer. Aedes aegypti and Aedes albopictus are not established. EEE is rare. Crater Lake and the high Cascades stay too cold for sustained transmission. Biting season runs June through September.
Snapshot of the current mosquito situation in Oregon, drawn from CDC ArboNET surveillance and the regional risk model.
- Risk Level
- Low
- Peak Activity
- May through October
- Dominant Vector
- Western Encephalitis Mosquito (Culex tarsalis) east of the Cascades and dominant WNV vector
Where Mosquitoes Breed in Oregon
Oregon mosquito habitat is built on the eastern irrigation grid and the Willamette Valley wetlands. The Columbia Basin in Umatilla and Morrow counties around Hermiston and Boardman holds the densest Cx. tarsalis populations in the state, with center pivot circles, dairy lagoons, and tail-water ponds producing sustained summer biting. The Klamath Basin around Klamath Falls and the Malheur National Wildlife Refuge in Harney County carry closed-basin marshes that feed bird-amplification cycles behind regional WNV. The Snake River corridor through Ontario holds irrigated alfalfa and pasture habitat. The Willamette Valley produces seasonal Aedes vexans off floodplain wetlands and steady urban Cx. pipiens through the Portland, Salem, and Eugene storm drain grid. The Oregon coast stays cool and dry through summer.
Hotspot Counties & Areas
- Umatilla and Morrow counties (Columbia Basin irrigated agriculture, WNV focus)
- Malheur County (Snake River corridor, Malheur NWR)
- Klamath County (Klamath Basin closed-basin marshes)
- Multnomah County (Portland metro)
- Lane County (Eugene, Willamette Valley)
- Marion County (Salem, Willamette Valley)
- Washington County (Hillsboro, western Portland suburbs)
- Eastern Oregon high desert irrigation belt
Seasonal Activity Pattern
Biting starts in mid June across the Columbia Basin and the eastern irrigated valleys as the irrigation cycle opens, peaks late July through August, and tapers through September. WNV cases concentrate in August across Umatilla, Morrow, Malheur, and Klamath counties. The Willamette Valley runs cool and dry through midsummer, with biting limited to dawn and dusk in shaded riparian corridors and around urban storm drains. Snowmelt off the Cascades and the Wallowas produces floodwater Aedes pulses through June on lowland river bottoms. The Oregon coast stays low-pressure year-round.
Monthly Biting Intensity (West Coast)
Oregon Mosquito Risk Profile
- WNV burden level
- Low
- about 5 to 15 confirmed cases annually
- EEE risk
- Rare
- Peak biting season
- June through September
- Top urban risk areas
- Portland (Multnomah)
- Eugene (Lane)
- Salem (Marion)
- Bend (Deschutes)
Signature habitat: Columbia Basin irrigated farmland, Willamette Valley wetlands, Klamath Basin.
Climate driver: Eastern Oregon irrigated agriculture drives WNV; western valleys see modest Culex pressure each summer.
Check Your Local Mosquito Risk
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Common Mosquitoes in Oregon
Understanding which mosquitoes are active in Oregon helps you identify threats and take appropriate precautions. Click any card for details.
Southern House Mosquito
Culex quinquefasciatus
Risk: West Nile virus, St. Louis encephalitis, dog heartworm.
Key feature: Medium brown body with banded abdominal segments and no leg stripes.
Active: Year-round in the deep South; summer peak elsewhere. Most active from dusk through the first few hours after sunset.
Yellow Fever Mosquito
Aedes aegypti
Risk: Zika, dengue, yellow fever, chikungunya.
Key feature: Black body with white lyre-shaped markings on the thorax.
Active: Year-round in southern Florida and the Gulf; summer-only further north.
Asian Tiger Mosquito
Aedes albopictus
Risk: Eastern Equine Encephalitis, dengue, chikungunya, Zika, dog heartworm.
Key feature: A single bright white stripe down the center of the back.
Active: Spring through first hard frost. Eggs overwinter in cold climates and hatch when flooded by spring rain.
West Nile Virus
Vector: Southern House Mosquito
West Nile Virus
The most common mosquito-borne illness in the US. About 80% of infections cause no symptoms; less than 1% develop neuroinvasive disease.
What to watch for
- Onset typically 2 to 15 days after a bite
- Most cases mild or asymptomatic, small fraction severe
- Neurological signs (severe headache, neck stiffness, confusion) need ER care
Breaking the Cycle in Oregon
The mosquito lifecycle takes about a week. These habits cut local biting pressure faster than anything else, building multiple layers of protection.
Drain the Yard Weekly
Empty buckets, planter saucers, kiddie pools, tarps, and clogged gutters. A week of standing water is one full mosquito generation.
Repel Before Going Out
EPA-registered DEET (20-30%), picaridin (20%), IR3535, or oil of lemon eucalyptus. Apply before going outside, especially at dusk and dawn.
Seal the House
Window and door screens with no tears. AC and porch fans both work. Mosquitoes struggle to fly upwind even at 1-2 mph air speed.
Treat Outdoor Clothing
Permethrin-treated long sleeves and pants for evening yard work, hiking, or fishing. Remains effective through 70+ wash cycles.
If You Develop Symptoms
Most mosquito bites are harmless. A small fraction can transmit illness, and knowing the timeline matters more than panicking at every itch.Five things to know.
Watch for fever
Fever, body aches, headache, or fatigue 2 to 15 days after a bite. West Nile often feels like flu, and most infections never get diagnosed.
Note where and when
A rough record of where and when you got bitten helps your doctor decide what to test for. Date, location, mosquito-heavy areas you visited.
Get help fast for neuro signs
Severe headache, neck stiffness, confusion, vision changes, or sudden muscle weakness can mean neuroinvasive WNV or EEE. Both are medical emergencies.
Pregnant exposure?
If pregnant and bitten in an area with documented Zika or local dengue transmission, mention to your OB. Same goes for travel exposure.
Children and seniors
Higher risk of severe disease from WNV, EEE, and dengue in adults over 60 and children under 5. Early call to the pediatrician or PCP if symptoms appear.
When does mosquito season end in Oregon?
Mosquito activity winds down after the first hard freeze, which in Oregon typically arrives around Oct 28. See the local first-frost window and city-by-city freeze dates.
Oregon first frost datesAlso worried about ticks in Oregon?
Lyme disease risk and tick activity track different seasonal patterns than mosquitoes. See your Oregon tick forecast.
View Oregon tick forecastStay Safe in Oregon
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