More than 300 homes have been evacuated in Florida amid fears a wastewater reservoir is about to collapse.

Florida governor Ron DeSantis declared a state of emergency after a leak was found in a containment wall of the Piney Point reservoir, which is 40 miles (64km) south of Tampa Bay.

The reservoir holds “primarily saltwater” from a dredging project and officials said its collapse could lead to 340 million gallons of water flooding out in a matter of minutes.

There are fears if the collapse happens, homes in the mostly agricultural area would be flooded with up to 6m (20ft) of water.

The Florida Department of Environmental Protection said the water is mixed with wastewater and storm water and has elevated levels of phosphorous and nitrogen and is acidic.

The ponds sit in stacks of phosphogypsum, a solid radioactive by-product from manufacturing fertiliser.

However, authorities have confirmed the water in the breached pond is not radioactive.

Mr DeSantis said: “What we are looking at now is trying to prevent and respond to, if need be, a real catastrophic flood situation.”

A highway in the area has been closed while families have been evacuated from at least 316 homes and placed in hotels.

Manatee County Sheriff’s officials have also been evacuating about 345 inmates from a local jail, the Tampa Bay Times reported.

Today I joined state officials in Manatee County who are actively responding to Piney Point and deploying all necessary resources. Please follow @FLSERT and @FLDEPNews for updates and monitor local alerts and evacuation orders. https://t.co/ACdrUdOkpO pic.twitter.com/ayOGoLR3Oo

Authorities have been trying to drain water away to reduce the risk of a breach since a leak was discovered in March. On Friday, the detection of a significant leak led to the first evacuations.

Scott Hopes, who is the Manatee County Administrator, said that using two pipes, 22,000 gallons per minute are being drawn “into a substantial drainage ditch which has conduits underneath two railroad tracks and then empties in a pipe to the seawall”.

There have also been attempts to plug the leak with rocks and other materials, but without any success.

Environmental groups have urged the federal government to step in to halt sending more wastewater to the existing so-called gypsum stacks and prevent the creation of more phosphogypsum, which is left behind when phosphate rock is mined to produce fertiliser.

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