Officials say the levee in San Juan Capistrano is dangerously compromised, with the concrete barriers on both side of Trabuco Creek crumbling away by raging waters.
The force of the water was so strong, the barriers were smashed to tiny pieces within seconds, with ragged holes and water pipes now exposed.
Witnesses say the raging torrent, fueled by all day rains, swallowed eight feet of the levee in the blink of an eye.
A neighborhood on the west side of the creek is at risk, with some homes less than a hundred feet from the edge.
400 people have been asked to evacuate, along with 75 businesses on the east bank, according to San Juan Capistrano Mayor, Sam Allevato.
Most residents have left their homes, just in case, in the meantime, a temporary fix is underway.
Giant boulders will be dropped into the two breeches to try to hold the water back.
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The concrete was laid in the area in the 1960s, according to San Juan Capistrano Mayor, Sam Allevato. A project to fortify them with steel walls has been underway, but it hasn't reached that far upstream yet.
"This creek does get swollen, and I've seen it almost crest this bank here," according to Sam Allevato, Mayor of San Juan Capistrano.
There was no cresting on Wednesday, but those levees must stay in place if that portion of San Juan Capistrano is to avoid flooding and more damage.
Another problem, looky-loos who got a little too close to the water which was rushing at 30 - 45 MPH.
Deputies had to rush in, and get people off of the dangerous levee.