Florida Governor Ron DeSantis declared the state of emergency on Saturday.
Another fear has been the water leaking or overflowing into Tampa Bay that is right next to it.
The evacuation order covers a half-mile radius south and a mile north of the abandoned Piney Point fertilizer plant wastewater holding reservoir, which could potentially dump hundreds of millions of gallons of wastewater on the surrounding neighborhoods, FOX 13 of Tampa reported.
Officials are trying to prevent "a real catastrophic flood situation" by ensuring the quality of the stack system as quickly as possible, DeSantis told reporters during a press conference Sunday.
Work crews were pumping millions of gallons of contaminated wastewater into an ecologically sensitive Florida bay on Sunday, as they tried to prevent the "imminent" collapse of a storage reservoir at an old phosphate mine.
"According to on-site engineers, a controlled release was necessary to prevent a catastrophic failure", the governor said.
"The water meets water quality standards for marine waters with the exception of pH, total phosphorous, total nitrogen, and total ammonia nitrogen".
Environmentalists are reportedly concerned a breach could kill fish, exacerbate red tide and lead to algae blooms.
The waste product from manufacturing fertiliser is radioactive, as it contains small amounts of naturally occurring radium and uranium, while the stacks can also release large concentrations of radon gas. "We can take care of nutrients in the environment ..."
"The immediate evacuation of residents, disruption of families during Easter weekend, and potential environmental catastrophe requires the attention and action of Florida's statewide elected leadership", said Fried.
"Evacuate area NOW. Collapse of Piney Point stack imminent!"
Florida's agriculture commissioner, Nicole Fried, wrote to DeSantis, saying the current emergency was only the latest in a string of incidents.
"For more than 50 years, this central Florida mining operation has caused numerous human health and environmental disasters and incidents", she wrote, adding there had been several earlier failures of the reservoir's lining.
Scott Hopes, the acting administrator of Manatee County, warned on Sunday that modelling had suggested a full breach of reservoir walls would release a surge "as high as a 20-foot wall of water" into the area.
An estimated 390 million gallons of water remained in the pond as of Saturday morning, according to the Florida Department of Environmental Protection.
This will "probably include filling these ponds after they have been devoid of their contents and capping them".
DeSantis said the company operating the site, HRK Holdings, should be held accountable.
"This is not acceptable and it's not something we will allow to persist", he said.
HRK did not immediately respond to a request for comment.