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Manatee County officials say the latest models show that a breach at the old phosphate plant reservoir has the potential to gush out 340 million gallons of water in a matter of minutes, risking a 20-foot-high (about 6.1-meter-high) wall of water.

Manatee County Sheriff's officials began evacuating about 345 inmates from a local jail about 1 mile (1.6 kilometers) away from the 77-acre pond first floor on Sunday afternoon, the Tampa Bay Times reported. Manatee County Administrator Scott Hopes said models show the area could be covered with between 1 foot (30 centimeters) to 5 feet (1.5 meters) of water, and the second floor is 10 feet above ground.

The Florida Department of Environmental Protection says the water in the pond is primarily salt water mixed with wastewater and storm water. It has elevated levels of phosphorous and nitrogen and is acidic, but not expected to be toxic, the agency says.

Crews have been discharging water since the pond began leaking in March. On Friday, a significant leak that was detected escalated the response and prompted the first evacuations and a declaration of a state of emergency on Saturday. A portion of the containment wall in the reservoir shifted, leading officials to think a collapse could occur at any time.