More than 300 homes in the area have been ordered to be evacuated, and a motorway near the Piney Point reservoir has been closed off.

Residents were sent a text alert telling them to leave home immediately.

Officials said the 77-acre (31-hectare) reservoir holds millions of gallons of water containing phosphorous and nitrogen from an old phosphate plant.

The pond where the leak was found is in a stack of phosphogypsum, a radioactive waste product from the manufacture of fertiliser.

The water contains small amounts of naturally occurring radium and uranium, and the stacks can also release radon gas.