The very act of going to a stream, walking in it, and fishing in it causes damage to some extent. Dislodging rocks thereby evicting nymphs and other critters from their homes, trampling vegetation, kicking up sediment and sending it downstream, stressing fish, on and on and on. It is not so simple for a whole lot of fishermen to purchase expensive new equipment on the whim of waterways "managers".
I have seen ducks and geese swimming, feeding, and waddling around in algae blooms and yes even on wads of rock-snot. I have seen the same creatures take flight, and in one instance touch down on a pond about 500 yards from the stream... unquestionably transferring biologic material between the waterways.
It's ridiculous to think fishermen are the primary vector. Yes, do whatever you can to decrease the spread, but live in the real world.
As I said before, I don't care at all about felt-soled boots. I've fished in a LOT of places (including Alaska) and the one pair I owned I didn't like. Never felt at a disadvantage with non-felt boots.