Sure, but there was a lot more available water in the watershed then also. Agriculture in a lot of ways has been the biggest ecological disaster this planet has ever seen. Man has redirected and pushed water out of nearly every watershed on the planet vastly changing what biome a area can support. I say that fully aware of the benefits that Agriculture has allowed human society, I wouldn't change it if I could in the past but I deeply hope we figure out a way to co-exist with nature in a less destructive way.