Euhm, I would say it's the opposite. Environmentalists will oppose dykes and infrastructure, because they will remodel the natural environment around the coastl

Euhm, I would say it's the opposite. Environmentalists will oppose dykes and infrastructure, because they will remodel the natural environment around the coastline and make it artificial and managed by human interference (which is of course, the very point of having them, so it's absolutely non-negotiable, beyond carving out a few reserves maybe).