Free Will… again

The physical non-living world around us is governed by the laws of nature. Water, due to the force of gravity, will move from a point of higher elevation to a point of lower elevation if it is permitted, but what if humans come along and erect a dam or divert the flow of water to go somewhere else? When we humans do something to our environment, is that action a complex manifestation of the physical and chemical laws of nature or are we separated from the non-living world in the sense that we choose to take a specific course of action through our own volition and free will? Does free will only exist for humans?