In Pico Rivera, the Whittier Narrows Dam stands like a guardian between the San Gabriel Mountains and the cities downstream from them. Its job is to make sure storms don’t become floods. But government studies show the dam may not be strong enough.

In recent public hearings, the U.S. Army Corps of Engineers said the 62-year-old dam no longer met the agency’s tolerablerisk guidelines and could fail in the event of a rare very large storm, such as the one that devastated California more than 160 years ago according to reports from the Southern California Partnership for Jobs.

And, according to the U.S. Geological Survey, the odds of a megastorm that could wipe out the Whittier Narrows Dam, as well as the Santa Fe Dam in Irwindale, are increasing as a result of climate change.

Scientists call this rare storm system California’s “Other Big One,” and say it could cause three times as much damage as a major earthquake. The storm could last for weeks and send more than 1.5 million people fleeing as floodwaters inundated heavily populated cities from Pico Rivera to Long Beach. Officials estimate the structural and economic damage would amount to more than $725 billion.

Specifically, federal engineers found that the Whittier Narrows structure could fail if water were to flow over its crest or if seepage eroded the sandy soil underneath. In addition, unusually heavy rains could trigger a premature opening of the dam’s massive spillway on the San Gabriel River, releasing more than 20 times what the downstream channel could safely contain within its levees.

Among the communities hardest hit in a dam failure would be Pico Rivera, a city of about 63,000 people immediately below the dam. In a worstcase scenario, Pico Rivera could be hit with water 20 feet deep; Downey could see 15 feet of water; and Santa Fe Springs, 10 feet.

The Corps is seeking up to $600 million in federal funding to upgrade the 3-mile-long dam, and say that due to the risk of “very significant loss of life and economic impacts,” the project has been classified as the agency’s highest priority of any of the 13 “high risk” dams in the country.