The fogging, weather permitting, will take place between 8:30 p.m. and midnight using Pyrenone 25-5 insecticide applied at a rate of 0.75 ounces per acre.
The decision to fog those areas came after two groups of mosquitoes trapped in Oakley tested positive for the virus, district officials said.
The first of the two locations to be treated is bordered by Contra Costa Canal on the north, Sellers Avenue on the east, East Cypress Road on the south, and Marsh Creek on the west.
The second location is bordered by East Cypress Road on the north, Sandmound Slough on the east, Rock Slough on the south, and Bethel Island Road on the west.
In Contra Costa County, 12 dead birds, eight groups of mosquitoes and two squirrels have tested positive for West Nile virus so far this year. No human cases have been reported.
For information about human West Nile virus symptoms, prevention or testing, please call Contra Costa Health Services at (888) 959-9911.
Map of areas to be fogged