As a precaution, workers are trying to plug breaches in the reservoir as well as pumping out thousands of gallons of water to minimise the threat.
The water being discharged is mostly seawater from the Port Manatee dredge project, process water and storm water, officials said. 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.
"So if you are in an evacuation area and you have not heeded that, you need to think twice and follow the orders", said Hopes at a news conference with DeSantis.
The 480-million wastewater reservoir has been leaking for days, but by 10:30 a.m. engineers "deemed the situation to be escalating", Manatee County Public Safety Director Jacob Saur told the newspaper.
"We are talking about the potential of about 600 million gallons (2.3 billion litres) within a matter of seconds and minutes, leaving that retention pool and going around the surrounding area", he said.
"This could have been resolved over two decades ago", Hopes said. "Evacuate area NOW. Collapse of Piney Point stack imminent!" "We are not out of the critical area yet".
Hopes says that if the pond collapses, there is a risk it could destabilise the walls of other areas in the plant.
The Florida DEP Secretary Noah Valenstein said another pond has higher levels of metals. We saw ducks yesterday, there are snooks swimming in there.
The U.S. Environmental Protection Agency has a co-ordinator on the scene co-ordinating with emergency management to provide support as necessary, said EPA spokeswoman Brandi Jenkins.
The pond where the leak was found is in a stack of phosphogypsum, a radioactive waste product from the manufacture of fertiliser.
"There have been numerous, well-documented failures - which continue today - of the property's reservoir liner, including leaks, poor welds, holes, cracks, and weaknesses that existed prior to purchase by the current owner, HRK Holdings, and exacerbated since", she writes.
"The pond is basically salt water".
Environmentalists are reportedly concerned a breach could kill fish, exacerbate red tide and lead to algae blooms.
There are at least 70 gypsum stacks in the U.S. and about 27 in Florida, mostly in the region of west-central Florida.