Elevation data collected at 80 sites in the canyon--primarily at pools just upstream of major rapids--suggest that the debris
damming those pools is on average 26 centimeters higher now than it was when those same spots were surveyed in 1923.
Similarly, fisheries that are sustained by flooding undergo an estimated 30-70% decrease in output with resulting losses in food and income as a result of
damming, according to the Food and Agriculture Organization of the United Nations.
Bureau of Reclamation, gave a speech lambasting environmentalists for their opposition to
damming up the Grand Canyon national park.