Depending on how long the river has been dammed up, tearing it down can have reverse ecological consequences now. It only takes about a decade for the downstrea

Depending on how long the river has been dammed up, tearing it down can have reverse ecological consequences now. It only takes about a decade for the downstream to adapt to the limited water flow (or the alternative interpretation is everything dies off within a decade) but after that to reintroduce the full flow would destroy new life that has settled the new environment produced.