I read a while back that the lake created from the dam is so huge it has changed the weather patterns of the surrounding area............More rainy............
Depending on how full, the dam also slows Earth's rotation speed lengthening the day, changes Earth's wobble and pole locations, makes the Earth fatter at the equator while bringing the poles closer, slightly causes world-wide climate change, as well as alters the distribution of gravity, how much things weigh, and the speed of time. All these changes are tiny but lab instruments can measure them.