It appears as though most of the heavy infestation is close to shore. Maybe some manual harvesting with a stiff rake would help get things moving. Re: catalpa trees, they should be getting worms on them if they are going to. The one that is dieing, could it be because it gets worms which defoliate it? If so, I bet that is a popular spot for the fish.
Maybe you can just trim them back severely to help prevent excess transpiration and growth.
