Damming and other methods of "harvesting" tidal power will always come with inherent drawbacks to the ecology that relies on that river flowing. When its a small personal use one like a water mill there probably isn't any damage worth mentioning, but getting any amount of power to be worth hooking to the grid will require huge installations. Maybe someone more of an expert can correct me, but that's what I've seen discussed when it came to harvesting the Mississippi back home.

So its still in the "personal usage is fine, government usage is damaging" category like the rest.