There's speculation that it could be blood or even some strange bacteria breeding in the waters - but it's just cordial or red dye that's been turning the Mission Bay fountain red.

Auckland's Council's head of operational management and maintenance community facilities Agnes McCormack said contractors had been down to check the fountain following reports of a change in colour at the harbourside pool.

"It appears someone has put a bottle of cordial or red dye into the water," McCormack said.

"Unfortunately this isn't uncommon, but we have fenced it off as a precaution until our contractors are able to access the underground services and clean it out."

Advertisement

Yesterday, the change in the water's colour did not deter from people taking a dip at the suburban Auckland attraction.

Many frolicked in the fountain as temperatures in the city soared into the mid-20s.

But the facility is closed today until after the fountain gets cleaned out.