Two otters have been killed in nets illegally set in a river at a nature reserve on the River Hull, Humberside Police has said.
The pair were found by walkers at the High Eske Nature Reserve at Tickton, near Beverley, on Thursday afternoon.
Fishing nets, which are prohibited in the reserve, had been placed in the river and a nearby pond to catch eels, officers said.
The otters appeared to have been dead for some time.
Sgt Dave Jenkins, of Humberside Police, said: "I have lived in this area all my life and spent a lot of time along the banks of this river and never had the pleasure of seeing an otter.
"They are something of a rarity, so to find two dead ones is quite devastating to the reintroduction of otters into this area.
"What makes matters far worse is that their deaths were totally unnecessary."
The force are now working with the Environment Agency and RSPCA to try to catch the offenders.