That's Plymouth harbor. They seem to have EEE outbreaks every decade or so. When I was a kid I asked my dad if they could get rid of it by getting rid of the horses.
It's funny how the insects we want to get rid of, like mosquitos, are indestructible despite billions of dollars devoted to killing them, yet we have to spend the same amount of money to protect decent insects, like bees, which are fragile and die off in huge numbers for no apparent reason.