Health warnings have been lifted at a popular Christchurch swimming spot after a septic tank overflow, caused by bottles being flushed down toilets.

Corsair Bay, near Lyttelton, was abruptly closed on Saturday after beachgoers reported a strong and unpleasant smell, prompting fears of a sewer leak and potential health risks.

Health New Zealand issued a public health warning after being notified of “a discharge of untreated sewage into Motu-kauati-iti Corsair Bay”.

However, the latest water testing showed faecal bacteria levels were now “below guideline values”, allowing the warning to be lifted and the water deemed safe for recreational use.

“This is great news for swimmers and other recreational water users who would have been avoiding the water following the high levels of contamination,” said Dr Cheryl Brunton, Medical Officer of Health for the National Public Health Service.

Christchurch City Council said investigations revealed issues with the site’s septic tank system after bottles were flushed down toilets, along with a malfunctioning outdoor shower that discharged clean water down a nearby pathway.

“Investigations identified a blockage in the septic system caused by items such as bottles, which led to an overflow into a small holding tank,” the council said.

“Concurrently, a fault in the outdoor shower resulted in clean water being discharged down the pathway. The effect of any combined runoff into the bay on water quality is inconclusive.”

Corsair Bay, near Lyttelton.

One would-be swimmer told the Herald they noticed an “ungodly, heavy smell” as soon as they opened their car door on arrival at Corsair Bay on Saturday.

Video footage shows a small stream of water flowing down a path towards the beach from a leak near a toilet block, where a puddle can be seen bubbling.

“Other people were commenting on the smell,” the witness said, adding that it “had me retching”.

The council said it has been working with Environment Canterbury (ECan) to carry out appropriate water quality testing.