The city Health Department will be spraying throughout all five boroughs this week to reduce the number of mosquitoes and the risk of West Nile virus.

The Department of Health says it is getting ahead of the season and will be spraying mosquito breeding grounds normally found in marshes and wetlands throughout the city.

It's expected to end Friday. 

The process is called aerial larvicide, and it works by flying a helicopter fairly low to the ground and spraying a portion of the larvicide as it flies over nonresidential areas. The larvicide isn’t harmful to humans, but it is proven effective to kill young mosquitoes before they grow into adults.

The Health Department has been monitoring mosquitoes that carry the West Nile virus, and, so far, there have been no cases reported this season.

Some of the locations where spraying will occur include Marine Park and Fresh Creek Basin in Brooklyn, and the Bronx will include Pelham Bay Park both north and south.