A trap knocked together out of swimming pool noodles, piping and mesh could be just what the experts ordered to stop turtles becoming the new koi carp.

Increasing numbers of escaped or dumped turtles around Northland waterways have prompted Northland Regional Council (NRC) to trial the new trap — and it could literally mean the slippery slope for the pet-cum- pest.

A bait tower in the middle of the floating trap lures turtles in but the surface they have to scramble over is too smooth and slippery for them to climb out again.

The council is still testing the prototype trap and will wait until the next turtle sighting is reported to deploy it.

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Turtles can do extensive damage to native fish and plants if left uncontrolled. Those living on the wildside are either pets that have wandered off or have been deliberately — and illegally — released.

"Turtles are a very tricky pest to catch given their ability to move in and out of waterways and stay underwater for long periods," NRC biosecurity manager Don McKenzie said.

There is no official estimate of how many turtles now live in the wild but local reports and sightings of them – especially red-eared slider turtles, officially classed as one of the world's top 100 most invasive species – have noticeably increased, McKenzie said.

Over the past two years, four live turtles have been handed in to biosecurity staff in Northland.

"Whereas a few years ago we probably wouldn't have received any sightings at all, it's not uncommon for us to receive several a year now, " McKenzie said.

The trap council biosecurity staff recently built and have been testing is based on an American design.

NRC chairman Bill Shepherd said he is impressed with the practical simplicity of the roughly metre-wide trap, put together in just a few hours and at little cost using a combination of PVC piping, mesh and popular children's swimming pool toys.

McKenzie said escaped turtle's eggs were unlikely to be viable in Northland's environment and the long-lived species unlikely to live beyond several years in the wild due to shell infections. However, the population is continuously being boosted through escapes or illegal pet releases.

Those turtles predate on nestlings of ground birds, skinks, frogs, fish and vegetation, he said.

Pet turtles must be kept in a secure area at all times to prevent accidental escapes and if someone can no longer care for a turtle, releasing it into a nearby stream is not an acceptable – or legal – solution, McKenzie said.