Whether or not you know it, almost all of us have a waterbody within 50 miles that has one specific non-native species. It isn't a parasite, although it sucks the good fishing out of many once-storied lakes and rivers. It isn't a fish or a bug or a snail, either. It is a plant.
Hydrilla is probably the most widespread invader in Oregon. It is that nasty green weed that has a swirling shaft that grows underwater. It is used in aquariums, but it ruins fishing areas. Furthermore, idiots put into ponds and lakes, because they think it will provide better cover for bass. It does, but it quickly chokes out all native vegetation and blankets the bottom of the lake or pond.
It is horrible to see once-pristine Cascade lakes covered in this disgusting mat of vegetation. Hyatt Lake is the perfect example of this. As the hydrilla dies, it decomposes, depleting oxygen, and raising the water temperature. It then floats to the surface, causing an unsightly breeding ground for mosquitos.
Hydrilla is an unforgiving monster of a plant that destroys every ecosystem it touches. So the $5 permit fee you have to pay for you pontoon boat is just a drop in the bucket to control this nightmare, and it is worth paying it 50x over if it keeps just one lake or river or stream free of this curse.