JenAjd, when Lake County sprays they are spraying for "mosquitoes and other biting arthropods of public health importance in order to reduce the risk of arboviral disease transmission and to ensure a reasonable quality of life for all residents and visitors of Lake County."
The program isn't just a random spraying either. They do research with collection trap devices to determine where and when to spray. The gnats you are seeing aren't affected by the malathion and permethrin insecticides. The gnats are not of any public health importance and part of the arboviral disease transmission targeted by the spraying.
They are a nuisance to some people, but not a public health problem.
http://www.lakecountyfl.gov/departme...anagement.aspx