Of course. Do anything and you create new ecosystems. Building the Maine dam in the first place created new ecosystems. They just aren't (1) beneficial to us in any meaningful way and (2) represent notable loss of a pre-existing ecosystem we value and want to preserve.
I don't see the hypocrisy there. You're trying to treat this as an absolutist thing (e.g. "riparian environments must be maximized at all costs") and color it as "reactionary environmentalism", when the truth is that it's a value judgement with specific evidence (e.g. "we fucked up the Kennebec river and we should fix that shit").
 More properly, given the article that no one here seems actually interested in reading: "We fixed that shit 20 years ago and, wow! It's fixed even better than we hoped!"
Your argument only seems to work if you start by assuming bad faith on the part of environmentalists. How about you trust us instead?
But there's a reason the article keeps using the word conservationist instead :)