The rich fisheries of Tonle Sap, the largest freshwater lake in Southeast Asia, largely supply the impoverished country's protein. The lake is unusual: It all but disappears in the dry season and then expands massively as water flow from the Mekong backs up when the rains come. "Those fish are so important for their livelihoods, both economically and nutritionally", said Gordon Holtgrieve, a professor at the University of Washington who researches Cambodia's freshwater fish and he points out that none of the dams that are either built or being built on the Mekong river "are pointing at good outcomes for the fisheries".