I've been on a camping trip for the past few days (I wrote and pre-posted Sunday - Thursday posts), and I've got some interesting water-related photos [click to see full size].
The first two are from what's left of Owens Lake, a "dry lake" that got that way when LADWP exported most of the water in Owens Valley via the LA Aqueduct.* As you can see, the lakebed is the source of (unhealthy) dust that blows all over the place on windy days. LADWP is -- under court order -- trying to minimize the dust by spreading enough water to keep it in muddy form (second photo). As far as I can tell, they are not succeeding.
This third photo is of Mono Lake, which almost went the way of Owens Lake. LADWP (again), was exporting a lot of water from the area and the lake level was dropping. As water levels dropped, the volcanic island in the photo -- a site of nesting birds -- was linked to the shore via a landbridge, and predators started eating all the eggs and young birds. The environmentalists won a court order that now requires that Mono Lake remain above a certain level -- to keep that landbridge underwater.
Bottom Line: Water exports can devastate places left high and dry. It is for this reason that water rights are tricky: Excessive transfers can destroy the environment. These examples do not mean that water rights, trades or exports are a bad idea. They only serve as a reminder that (1) water transfers should be implemented gradually and (2) water transfers from area of origin should probably be capped at some level consistent with the steady-state environment. (I am explicitly excluding "origin" areas that have water brought from elsewhere, e.g., Imperial Valley.)
* These exports started in 1913 and are important to the plot of the movie Chinatown (1974), a film that combines two stories: Los Angeles' 1915 annexation of the San Fernando Valley and lobbying for the Colorado River Aqueduct in early 30s. In the film, water managers dump water to create a "drought" and scare citizens into paying for an expensive project to import water. After the project is built, the dumping stops and the new supplies (now surplus) are suddenly available to outlying areas that the water managers (conveniently) bought for pennies. The managers get rich, and the hero (Jack Nicholson) is disillusioned by their abuse of power.