The US$626M Lower Colorado River Multi-Species Conservation Programme is intended to keep healthy 26 species of fish, plants, birds and other animals along the 643km of river below the Hoover dam running through the three states.

The conservation effort is designed to ensure water agencies can continue their water and power operations on the river unburdened by concerns about threatened and endangered species.

Environmental groups are critical of the plan as it does not include the 161km of the river that flows through Mexico. But US officials said it would be impossible for them to control conservation activities across the border.