Until I know more, here is the Homepage of the Sierra del Lacandon Regional Archaeology Project.
It has a terrific summary of the dam situation, with maps, called Threat of Dams on the Usumacinta River
And thanks to his resources:
This new article in Archaeology Magazine on dams in the Mundo Maya.
And this pdf file from The Center for Governmental Responsibility at the University of Florida's Levin College of Law: The Usumacinta River: Building a Framework for Cooperation Between Mexico and