I have been watching magnet fishing and people love to toss stuff over bridges without a second thought on the environmental impact. Hiding evidence I can almost understand but not lawnmowers, car batteries, etc.
It seems deeper fines should be made to discourage this terrible behavior.
Lack of proper disposal facilities and/or fees for using said facilities. Easier to dump something in a lake or in the bushes than driving 40 minutes across town to a special facility and paying $30+ to dispose of it properly.
Everyone who disposes properly has to pay a fee. The only ones who have to pay the fine for dumping are those that get caught.
Solution: turn responsible disposal into a game, where if you can successfully sneak your trash to the correct section of the disposal center without anyone noticing, you get paid the amount you would have had to pay as a fee.