Flood control means that the areas downstream now do not live under constant flood danger. HEP is clean electricity from a renewable source and does not contribute to the greenhouse effect.
Salinity increases due to high evaporation with the large surface area of the lakes exposed to the hot desert sun. The Colorado salt level increases from 200 parts per million at its source to 6500 parts per million at its mouth.
In 1990 the USA had to spend $300 million building a desalination plant at Yuma. Construction of the plant was completed in 1992 and it has operated on just two occasions since then.
According to the US Bureau of Reclamation, the plant has been maintained, but largely not operated, due to surplus and then normal water supply conditions on the Colorado River.
Rainbow Bridge, an important geological site is being slowly destroyed.
Increased evaporation rates means that lots of water is lost every year, Lake Powell loses 0.74 km3 annually.
Seepage is a major problem with Lake Powell losing 300 km3 annually.
Groundwater has to be used in many areas to top up the river and honour the terms of the Colorado Compact. The use of groundwater is unsustainable.
Many plants and animals were lost as the lakes flooded. Beavers for example disappeared from Tucson as the rivers dried up.
The delta of the river has turned into a lifeless salt marsh, abandoned by the birds and animals that once lived there.