A chance discovery on Saturday (15 Jul) of a temporary public health warning sign on Te Anau's lakefront caught authorities unawares and created concerns within the Fiordland tourist town.

The Southland District Council (SDC) sign, near the RealNZ wharf, warned that it was not safe to swim, collect shellfish or conduct other water activities.

It also advised that the sign would be removed once water quality improves.

John Carter, a keen lake swimmer and member of the marine rescue team, discovered the threatening sign on Saturday (15 Jul) while paddle boarding and diving.

"We rave about the drinkable lake."

"To me it's a sign that is a little bit out of place."

"I usually swim from Dusky Street down to Real Journeys [RealNZ], sometimes I'll swim to DOC [Department of Conservation] and back."

"If there is a problem with that water, we should be treating the storm water rather than discharging it into the lake."

Carter said the lake was well used, with over 100 regularly swimming as part of the local open water swimming group.

SDC water and operations manager Geoff Gray said that after investigation he could confirm that the sign was erected approximately 5 years ago, after a plumber had mistakenly misconnected the stormwater and sewage connections during a new build.

That incident had resulted in toilet paper and human waste going out the pipe, he said.

Gray said he was currently having a new water test done, with the results expected early next week (24 Jul).

"If they're clear, that sign will be removed," Grey said.