A possible second leak has been found in a Florida wastewater reservoir that risks flooding nearby communities with millions of gallons of contaminated water, authorities said Monday.

"An infrared drone identified a signature that could indicate a second breach" at the Piney Point reservoir on Tampa Bay, said Jake Saur, public safety director in Manatee County in the west of the state.

Engineers were studying the new data, he said.

Emergency workers, assisted by the Florida National Guard, have been pumping about 33 million gallons of water daily out of a wastewater reservoir at the site, which has sprung a growing leak in its plastic lining.

More than 300 homes near the site of the abandoned phosphate mine and fertilizer-production facility were put under mandatory evacuation orders at the weekend, and Governor Ron DeSantis declared a state of emergency to free up funds to tackle the crisis.

Some prisoners from a county penitentiary have also been bussed to an undisclosed location, while others were moved to higher floors in the building.

The contaminated water was being pumped into Tampa Bay to avoid what authorities warned could be a "catastrophic" flood in the area.

The governor said the wastewater has higher phosphorous and nitrogen levels.

Marine algae thrive on such elements, and environmental groups fear the release of millions of gallons of nutrient-rich water into the ocean could trigger a deadly "red tide," or algal bloom, that can suffocate fish and other aquatic life and deter tourist activity.

Florida Republican Congressman Vern Buchanan said the situation was "very concerning" and called for the Environmental Protection Agency to step in.

A collapse of the reservoir also risked sending water into nearby stacks of phosphogypsum, a leftover from fertilizer production.

Phosphogypsum is considered radioactive as it contains isotopes such as radon, as well as toxic heavy metals like arsenic, lead and mercury.

© Agence France-Presse