Auckland's popular Takapuna Beach is closed to swimmers after pollution flowed into the water between the red and yellow flags.
Lifeguards shut the beach at 3.30pm on Monday, when a fault caused a stormwater drain to overflow.
The flags were taken down and the beach was closed for swimming for the remainder of the day — with the water quality labelled "high risk".
The Auckland SafeSwim website continues to regard the beach as high risk, saying there is an "elevated health risk due to poor water quality; temporary no-swim warning in effect".
Meanwhile, surf life savers are warning that 2-3m swells are predicted today for west coast beaches, bringing large surf and strong currents.
Hazard warnings are in place to alert beachgoers to the conditions.
People are being reminded to always swim between the flags at a lifeguarded beach.