Terrapins spotted basking in a Co Tyrone river are to be removed in case they breed and damage the ecological balance of the river.
Earlier this week the Belfast Telegraph revealed that two yellow-bellied sliders had been photographed sunbathing on a floating log in the River Mourne by 12-year-old Cora Madden.
The species is not native to Northern Ireland, so the animals are thought to have been released into the river, an offence under the 1985 Wildlife Order.
The Department of the Environment says non-native species can cause problems by feeding on local wildlife and staff are in the process of drawing up plans to remove the terrapins.
A spokesman said it is thought the climate is too cold for the terrapins to breed here so the removal is precautionary, but an invasive species expert at Queen's University Belfast said they are already breeding in the wild in England and have been named among the world's top 100 most invasive species.
A DoE spokesman said: "Northern Ireland Environment Agency will be working alongside our partners in the north west to assess how best to remove this alien species from the river.
"There have been reports of red-necked terrapins being released into ponds in the past in Belfast and Larne – however both populations were controlled and the terrapins removed. Current summer conditions in Northern Ireland would suggest that it would be too cold for them to breed here, but we would wish to take a precautionary approach."
But invasive species expert Professor Jaimie Dick from Queen's said: "A rapid response is needed. These are very predatory animals and they could have impacts on a whole range of invertebrates and even small fish. The elimination of those species could then affect other species that rely on them as food sources."
Stephen Foster from NIEA said staff are making an assessment of how the terrapins can be removed from what is a physically challenging site.
"Our priority is to nip it in the bud while the population is small," he said.
"These are at the lower end of the scale from the point of view of environmental impact, compared with other non-natives that have arrived here."
The yellow-bellied slider is a non-native species in Ireland. It has been introduced to many parts of the world primarily through escape or deliberate release as an unwanted pet. While this species is not believed to be able to successfully reproduce under current climatic conditions in Ireland, it can persist locally, competing with native species for food and resources. It can also impact on some nesting bird species by using nests to bask. There is also a risk of disease and parasite transmission to native species and humans.