A mystery pool pooper - or poopers - has struck again at an Invercargill swimming pool.

It is the sixth Friday in a row someone has defecated in a swimming pool at the centre.

In the first instance a "smidgen" of faeces was discovered in the leisure pool at the Splash Palace Aquatic Centre about 4.30pm.

JOANNA GRIFFITHS/Stuff.co.nz Splash Palace Aquatic Centre manager Pete Thompson speaks about the 'mystery pooper' who has plagued the pool for the past six weeks.

Aquatic Centre manager Pete Thompson said swimmers had been removed from the pool and extra chlorine had been added to the water but he believed this incident to be "an unfortunate coincidence".

"The mode is dissimilar to anything else we have had. It was a very tiny 10 cent piece-size which suggests it probably came out of a baby's togs," he said.

A second poo was done later. The learners pool was closed before 6pm when it was discovered.

The pool was expected to be closed for cleaning for half an hour before reopening.

Thompson said the second poo was extremely frustrating.

He did not know if the poos were deliberate.

"How do you prove something is deliberate unless you catch them in the act?

"I hope whoever this person is, if it's deliberate, ceases to behave in this manner. It's disgusting.

"If it's accidental I hope their parents educate them and hopefully we don't see this happen again."

Thompson, who has had to deal with poos in the Splash Palace pools for six weeks running, said he was tired and frustrated.

He was also annoyed for his staff and for the public.

"They are paying to use the pool and they aren't getting to use it."

Thompson noted the Dunedin swimming pool was closed today for the same reason.

"Some sort of coordinated attack around the country perhaps," he mused.

'IT'S PATHETIC'

Invercargill mother Lynda Gray, whose children do swimming lessons at the Invercargill pool, said the serial pooer was driving her nuts.

"It's pathetic... Just disgusting, we have had enough," she said when learning another poo had been done in the leisure pool tonight.

Her children's swimming lessons had been disrupted for the past five weeks due to the serial pooper.

Another mum at the pool, Kate McHugh, said the serial pooper was "just rude".

"It's a busy time at the pool, the kids look forward to it," she said as she surveyed the emptied out pool after the poo was found.

"I think, if it's deliberate, it's very disappointing."

Daryl Gray, who was watching his grandson in the water, said dozens of kids were in the leisure pool when the poo was done.

"The man came along and spotted something in the pool and came back with his pooper scooper net... then he closed the pool."

The pool was so busy it would be nearly impossible to spot the culprit, he said.

POOL ON POOP WATCH

Staff at Splash Palace had been on watch to catch the pool pooper who had hit the complex five Friday evenings in a row, normally after 5pm.

The culprit's actions have gained national and international media attention.

Previously, when the faeces were spotted the pool was closed for up to six hours at a time for cleaning, resulting in the swimmers being kicked out of the water.

Thompson said hundreds of kids from the Murihiku Swimming Club, school water polo teams and casual swimmers used the pools on Friday nights, making it difficult to spot the offender in action.

The pool complex had cameras, "but not high definition enough to pick up the red face of someone squinting", he said.

Murihiku Swimming Club president Hilary Strang said its more than 100 children who had swimming lessons at the pool on Friday nights had missed out on lessons due to the actions of the offender.

"Some of these families are from Riverton and Winton and they have to turn around and go home and it's been a waste of their time."

The culprit's actions were disgusting and she would like to know who it was, she said.

"I think it's an incredibly selfish thing to do. It affects so many people and it could be putting people's health at risk."

Southland Water Polo president Brendan Bowie said about 700 children from 68 school teams played water polo at the swimming complex on Friday nights. Senior players were unable to play water polo on one of the night's faeces were found in the pool.

Neither club boss had any idea if the offender could be from their club or was instead a casual swimmer, while some believed a nervous kid may be pooing involuntarily.