Although the government claims that spraying is targeted towards mosquitoes, their website admits that the chemicals are toxic to invertebrates and fish.
From the Mass.gov website:
No one loves mosquitoes. EEE is a rare, but deadly affliction. But, we should not poison our environment and risk our health in order to reduce our exposure to a relatively rare mosquito borne disease.
The answer is diversity! More bugs, not less. Balance, not elimination! Grow native plants! Encourage all insectivores! What’s good for the bugs, birds, and animals is good for us.