Investigations into the closure of a popular Christchurch swimming spot have found that a foul-smelling odour was caused by a septic tank overflowing after bottles were flushed down toilets. 

Corsair Bay, near Lyttelton, was abruptly closed on Saturday after beachgoers reported a strong, unpleasant smell, raising concerns about a possible sewer leak and health risks. 

Christchurch City Council said investigations have since identified issues with the site’s septic system and an outdoor shower, which discharged clean water down a nearby pathway. 

“Investigations have 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 malfunction in the outdoor shower also discharged clean water down the pathway. 

“The effect of any combined runoff into the bay on water quality is inconclusive.” 

The council said that it had contacted Environment Canterbury (ECan) to facilitate appropriate water quality testing. 

The council said that it had closed the carpark, toilets and track and was “working with contractors to repair the septic system and open facilities as soon as possible”. 

“The council will be undertaking water quality testing at Corsair Bay today and over the next few days at 2 – 3 locations within the bay as a result of the incident. 

“We have also been advised that ECan are testing the water quality today as part of routine testing.” 

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

“Water contaminated by human matter may contain a range of disease-causing micro-organisms such as viruses, bacteria and protozoa,” National Public Health Service’s Dr Imogen Evans said. 

Eating fish or shellfish from these sites should be avoided, Health New Zealand said. 

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”.