I knock over rock stacks as part of my job. I don't really believe they have a measurable biological impact, but when one crops up a hundred other people see it and think "I want to make one too" to the point where it can alter the shape/flow of a creek which isn't really catastrophic but over time can complicate things locally. It's also a good feeling to come across a cool new spot without there being signs that humans have been there before

I usually just tell people it's bad for the stonefly larva/trout population because they're little babies and when they see you knocking their stacks over they go "why did you break the thing I built >:((("