For five weeks in a row, one or more swimmers have defecated in a New Zealand pool with potentially malicious intent, costing the local council tens of thousands of dollars to replace the fouled water.

The “mystery” pooper, or group of poopers, perpetrated an especially egregious faecal attack last week, evacuating their bowels in a total of three separate pools, local media has reported.

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Splash Palace in Invercargill, located on the South Island, is the victim of the foul incidents, for which its operators want financial redress.

“If we do manage to, dare I say, catch someone in the act, we will seek compensation,” city council aquatic services manager Pete Thompson told The Southland Times.

Suspicion has reportedly fallen upon a group of athletes, whose regular visits on Friday afternoons align perfectly with the offending ploppers.

“It generally happens after 5pm each Friday night. There are certain sports groups that use the facility at that time of day,” Mr Thompson said.

It takes the facility six hours to clean the water after each of the incidents, which are believed to be “deliberate”, the media outlet reported.