Eye on LifeTV Show

The beaver builds a dam across a river: it changes the local environment, but it's small change compared to man. When he builds a dam, like the one at Kariba, the changes are monumental. The environment-ecological balance-is upset. Perhaps permanently by man's activities-only temporarily by the beaver. Can man continue to dam as the beaver does, without thought for the future? Or is more planning needed before major changes are initiated?