A lack of precision in the way I worded a post last week on reservoir levels in Lake Powell and Lake Mead seems to have led to some confusion.

I was writing about the rising levels in Lake Powell as Lake Mead was dropping, and suggested this was the result of a management decision rather than natural forces. But I did not mean to imply, as David argues, that this is the result of the two reservoirs being managed by two different Bureau of Reclamation offices.

Under the Colorado River Basin Project Act of 1968, the Secretary of the Interior is given the responsibility for joint management of the two reservoirs in a coordinated fashion. Operating rules have been developed for the joint operation of the two reservoirs, most recently codified in the Record of Decision for the 2007 shortage sharing agreement. That document sets the triggers for how much water is kept in Powell, and how much released to Mead. It’s operation under those rules, which Pat Mulroy and the other lower basin stakeholders helped develop, that has led to the see-saw of rising Powell and dropping Mead.

The disconnect is not in the river’s management, but in the resulting political conversation. In thinking about the river as a whole, it is most useful to think about the total amount water stored in both reservoirs. But in building a sense of urgency in Las Vegas, it is in Pat Mulroy’s interest that her community focus on Mead’s dropping levels.