The Environment Agency’s bathing water quality website warns people to stay out of the water at Heacham, near Hunstanton because of a “pollution incident”.
Both the village’s beaches had been plagued by poor water quality for years, before being rated “Adequate” last November.
“This bathing water is subject to short-term pollution procedures,” the latest warning says.
“The Environment Agency makes a daily pollution risk forecast at this site based on the effects of rain, wind and seasonality on bathing water quality.
“These factors affect the levels of bacteria that get washed into the sea from livestock, sewage and urban drainage via rivers and streams and how they disperse.”
After a short-term pollution event, the EA said bacteria levels usually return to normal within one or two days, though warnings may last longer.
Heacham’s coastal waters had been classified as “poor” by the agency between 2021 and 2025, with droppings from seabirds believed to be responsible for poor water quality.
Last November, the water quality was rated as “adequate” and given a one-star rating meaning it was safe to swim in.