Of course, any species outside of its home niche can become invasive, which is the case with red-eared sliders (Trachemys scripta), which I just think of a cute turtle common where I grew up, but, according to Đài Tiếng nói Việt Nam, the Vietnamese foreign-service broadcaster, they are a serious problem:
A dangerous invasive turtle species, the red-eared slider, was found living in Hồ Hoàn Kiếm lake in the centre of the capital city [Hà Nội] last week.Adding to the problem is that Hồ Hoàn Kiếm lake is home to Hoàn Kiếm giant softshell turtle (Rafetus leloii), an endangered species so rare that it's almost considered cryptozoologic.
"The appearance of the red-eared slider at a time when water levels are dropping and food resources are dwindling is a real danger," Professor Hà Đình Đức said.
The biologist said the species, Trachemys scripta, was native to the United States and was a popular pet in many countries, but is also listed as one of the 100 most dangerous invasive species in the world.
Some scientists believe the R. leloii in Hồ Hoàn Kiếm to be capitive specimens of the equally rare Yangtze giant softshell turtle (Rafetus swinhoei), which is believed to be extinct in the wild, according to Conservation International's "The World's Top 25 Most Endangered Turtles" [PDF].
According to legend, Lê Lợi (1385-1433) was loaned a magic sword by a giant turtle living in the lake, thus the scientific name R. leloii. After using the sword to drive Chinese troops from Việt Nam, Lê Lợi returned the sword to the turtle, which is why "Hồ Hoàn Kiếm" means "lake of the returned sword."