A ''faecal incident'' forced swimmers from the main pool at Hamilton's Waterworld last night.

Council general manager community Lance Vervoort said faeces were discovered at 6.10pm, the fourth time in two months a defecating swimmer has forced a closure.

''As per the procedure in line with Pool Water Quality Standards NZS 5286:2010, staff immediately closed the pools and removed the faecal matter,'' said Mr Vervoort.

''The pool was vacuumed, and spot chlorinated directly. Staff also increased the chlorine rate, and regularly tested the water to monitor chlorine levels,'' he said.



Management also decided not to re-open the pool until this morning.

''We can assure pool users we've followed all the required procedures after this incident, and are confident water quality is back to safe levels.''

Mr Vervoort said defecation was ''unfortunately common throughout NZ pools''.

Mr Vervoort said it was impossible to say if there was a serial defecator.

"We can't be sure if it's the same person. Identifying patrons responsible for these incidents is very difficult for our staff. People don't generally own up to it," he said. "The general belief is that people responsible are usually young children."