I have a good friend with a pond that has structure that's probably about 40% of his pond, and that's probably too much. The fishing is extremely difficult because the overall biomass of the pond is so spread out that it actually makes it harder to locate concentrations of fish. He certainly doesn't have any problems with predators of any kind. Also fishing is a pain in the rear, because you lose so much gear.
That is pretty much the situation in my pond. Islands of Elodea. The Elodea dies back in the winter and grows like mad spring through summer. By the end of summer I have it all along the shore and even islands in the middle. I have been able to treat it yet except for manual removal - which is a very short term solution. Anyway it doesn't slow down herons much they will wade into it and pick off fish.
I think that it would depend upon the type of vegetation cover.
I like the idea of the propane canon and it just occurs to me that a propane canon might also be useful in scarring trespassers (different thread).
