Fish usually found living in the waters of the Pacific and Arctic oceans have been discovered in the north-east of England.
Wild pink salmon, Oncorhynchus gorbuscha, have been caught in the River Tyne near Wylam and off the coast of South Shields.
Native to the North Pacific basin, the Environment Agency said it was "unusual" to find them in these waters.
The agency said a "major impact" on wild fish stocks was "unlikely".
Anyone who spots the salmon is "urged" to contact the agency with a date, location and if possible a photograph, to help build up a picture of where they are, the agency said.