First, I love the warning…to beware of something that is explicitly labelled as merely possible.
Most road signs don’t bother to assert the possible status of the hazard, and warn of actual hazards (“wind gusts”, “children crossing”, “wildlife on road”, etc.) leaving unsaid the fact that these are only sometimes present, or explicitly identifying the times they are present (“slippery when wet”).
Second, it’s a warning intended to enable drivers to avoid a hazard. Yet this warning is given at a place in the road where you are completely committed to continuing across the lake, so its a warning about which the driver can do very little, even if there are actual (not merely possible) swarms over the lake.
Often these are swarms of bugs that don’t impede visibility significantly, but will damage to a paint job of not cleaned off immediately. So slowing down doesn’t help much. You have just passed through a toll gate and paid your $2 to cross on the bridge, and so there is no exit or anything you can take. And you are not allowed to stop on the side of the road (you are on a toll highway bridge) except in an emergency.
Giving the warning before the previous exit would give the driver the option of taking the non-toll route around the late, at least. But the choice of the location of the warning sign makes any such choice impossible.