A black flag's been raised to stop swimming at a popular Auckland beach

Watercare warns there's a very high risk of illness from swimming at Long Bay Beach on the North Shore, due to a wastewater overflow.

In a post on social media, Watercare says it's not an ideal way to start the New Year and the warning is in place for the next 24 hours.

Aucklanders are urged to check the Safeswim website to check water quality at beaches and bays, before swimming this summer.