Aucklanders thinking of hitting up some popular beaches to avoid the hot and sticky weather are being warned to watch out for bluebottles and faecal bacteria.
On Monday, Safeswim updated its map of water quality and swimming conditions to show multiple beaches are unsafe to swim at.
Bluebottle jellyfish have been reported at the Auckland region's Karekare Beach and Bethells Beach.
Their venomous tentacles cause an extremely painful sting which raises red welts. These can last several days.
According to the Ministry of Heath, the best care for a sting is to flush the stung area with seawater then immerse it in heated tap water.
Serious allergic reactions are rare, however an ambulance should be called for symptoms including shortness of breath, severe dizziness or signs of shock.
Along the west coast, there's also the risk of large surf or strong currents at Muriwai, Bethells Beach, Piha North Beach and Piha Beach.
The Safeswim map uses water droplet icons to separate 'low-risk' beaches and 'high-risk' beaches.
Currently, Narrow Neck, Herne Bay, Home Bay, Te Tinana, Okahu Bay, and Mission Bay have 'black' water droplet icons, which warn of an overflow from the Watercare wastewater network.
"Wastewater overflows occur when wastewater (sewage) spills out from gully traps, manholes, engineered overflow points or pump stations. It then flows into backyards or waterways and the sea," the Safeswim site advises.
These wastewater overflows have a significantly higher public health risk than general stormwater contamination.
Watercare has multiple projects underway to reduce overflows, including expanding the wastewater network with projects such as the Central Interceptor pipeline, and building storage tanks to hold excess flows that would overload the network during heavy rain.
