Mosquito season in Island County, WA: when it starts and ends
Mosquito months in Island County
In a normal year mosquito season in Island County, WA starts around April 17 and ends around October 20, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Island County, and when
- Start tipping out standing water weekly by April 3.
- Book any yard treatment for mid April, ahead of the August peak.
- Repellent can go away after October 20.
- No West Nile cases since 2016, so bites in Island County are a nuisance; check window screens.
Island County against the rest of WA
Island County has the 9th longest season of 39 WA counties, at 186 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 50.8°F.
- Grant County: April 12 to October 16 (187 days, 0 WNV)
- Wahkiakum County: April 20 to October 24 (187 days, 0 WNV)
- San Juan County: April 20 to October 22 (185 days, 0 WNV)
- Mason County: April 20 to October 20 (183 days, 0 WNV)
West Nile in Island County
CDC ArboNET lists no human West Nile cases for Island County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.
More: how the dates are worked out · when the season starts across the US.