Nysse, whose taken charge of the turtle's care, believes it may have been released into the wild as people often purchase them as pets then release them when they get large.
A Facebook post to a lost pet's group on behalf of Theo asking for his owner has so far found no luck.
"I spent last night in a strange tub, I snacked on silver beet and apricots, but I would love to return back to my family as they know my favourite cuisines," the post read.
"If you're missing me, or know where my home is, please reach out to my human friends so they can take me home."
If the owner cannot be found Nysse is planning on creating a home for Theo in the small pond at her Havelock North home.
"If we can't find the owner he has a beautiful new home he can live in, I am planning on buying all the equipment he needs," she said.
Chris Wootton, senior ranger at DoC, said the turtle is a red-eared slider and was likely to be a pet.
He warned that they should not be released into the wild as Nysse expects it may have been.
"It is legal to own the turtle as a pet, but it is an offence to release these turtles into the wild as they can become pests," Wootton said.
The turtle is omnivorous and feeds on vegetation and small animals such as insects, molluscs, frogs, crustaceans, birds and small reptiles.
Red-eared sliders are a major potential pest in New Zealand and numbers may increase with climate change, Wootton said.
"This species is a 'ticking time bomb', much like several pest plants that are currently on the marginal edge of their climatic range in New Zealand," he said.
