OPINION: Tell the Dam Truth

As Colorado River management faces federal deadline, a new scientific report challenges ‘clean energy’ myth of Glen Canyon and Hoover dams

The new report from nonprofit group Tell The Dam Truth estimates the full lifecycle greenhouse gas (GHG) emissions caused by Glen Canyon and Hoover dams are equal to the average yearly emissions from 1.7 coal-fired power plants.

As the U.S. Bureau of Reclamation pushes forward with a comprehensive Environmental Impact Statement (EIS) to determine the “operations of Lake Powell and Lake Mead,” the report challenges part of the underpinning of the Bureau’s work.

The Bureau of Reclamation has stated that hydropower generated at the Glen Canyon and Hoover dams is “clean energy,” including on the webpage for Hoover Dam, where the agency states: “Hydroelectricity is a clean, renewable source of energy that does not result in air pollution … and is therefore beneficial to the environment.” Tell The Dam Truth’s report, however, estimates the dams are responsible for “approximately 6.48 million metric tons of CO2e/year, which equals the average yearly emissions from 1.7 coal-fired powerplants.”

Dams contribute to greenhouse gas emissions in many ways, including through the reservoirs and artificial lakes they hold back.  As vegetation decays under the reservoir’s surface, it releases greenhouse gases. The inundation area also loses its ability to sequester carbon from the air due to being artificially flooded. The Glen Canyon Dam system, which includes Powell Reservoir/Lake Powell, is estimated to be responsible for 1.78 million metric tons of CO2e per year. The Hoover Dam system, which includes Mead Reservoir/Lake Mead, is estimated to be responsible for 4.7 million metric tons of CO2e per year. Dams in general also destroy carbon-capturing habitats downstream, ruin life-sustaining fisheries and starve coastal communities of the sand and rocks critical to defending against rising seas.

“Among the biggest GHG impacts caused by Glen Canyon and Hoover dams has been the dry-up of the Colorado River delta in Mexico,” said Mark Easter, Tell The Dam Truth’s lead scientist. “Restoring portions of the delta’s wetlands would reverse that process and help turn the Colorado River system toward being a carbon sink instead of a carbon emitter.”

Over the last two years, Tell The Dam Truth created the All-Res Modeling Tool, which estimates lifecycle greenhouse gas emissions for dam and reservoir systems. The tool was first deployed on the proposed Sites Reservoir in California and subsequently on the four Lower Snake River Dams. This third deployment – on Glen Canyon and Hoover dams – is intended to engage with Reclamation’s EIS process for the management of the Colorado River. The tool takes into account the best available science and includes all of the greenhouse gas emission source categories documented in peer-reviewed scientific literature attributable to any dam and reservoir system including hydropower facilities.

Glen Canyon and Hoover dams do not produce clean or carbon-free energy. The Bureau of Reclamation must stop greenwashing these energy sources. Further, states like California, that import vast amounts of Colorado River water and electricity, need to account for these emissions in their GHG inventory programs.

“As the Colorado River EIS process moves forward, we encourage the Bureau of Reclamation to take a hard look at the significant climate emissions caused by dams,” said Greg Curtis, Executive Director at Holdfast Collective, which funded the development and deployment of the All-Res Tool. “If we want to get serious about the climate crisis as a country, and in states like California, we must bring the best science to measure and evaluate climate impact at all energy facilities to enable clear-eyed decisions going forward. The changes recommended by this EIS will shape the river’s management and the natural landscape for decades. Holdfast Collective is excited to fund this effort and help bring accountability and transparency to the carbon-emitting dams and reservoirs on the Colorado River.”

On January 17, 2025, the Bureau of Reclamation announced the “alternatives” for the EIS which were discussed at the annual Colorado River Water Users Association meeting in December in Las Vegas. None of the alternatives consider or discuss the GHG emissions caused by Glen Canyon and Hoover dams. The Draft Environmental Impact Statement is expected to be released in coming weeks.

The full All-Res report for Glen Canyon and Hoover dams is posted here.