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Condition of thousands of U.S. dams kept secret in national database despite increased transparency

The condition ratings of thousands of dams across the U.S. remain a secret despite changes to improve the transparency of a national database.

The U.S. Army Corps of Engineers used to withhold condition assessments from its National Inventory of Dams because of security concerns stemming from the Sept. 11, 2001, terror attacks.

Under a recent policy change, condition assessments and hazard ratings are available for more than one quarter of the 92,000 dams in the inventory.

However, the Corps still allows federal agencies and states to keep some information confidential. That means conditions still aren't being made public for some of the nation's biggest dams.

Approximately 130 of Arizona’s more than 400 dams are classified as having high hazard potential, according to the University of Arizona’s Water Resources Research Center.