Otters have been found drowned in illegal crayfish traps in the River Waveney on the Norfolk/Suffolk border.
The Environment Agency said it had been alerted to three incidents recently.
The latest discovery was by a member of the public who spotted a trap with a dead otter in it floating in the river at the entrance to a yacht station.
The crayfish trap had no otter guard. The opening was large enough to allow an otter to get at the bait and it drowned when it could not get back out.
Otters on the Broads have also suffered recently at the hands of someone setting a fyke net, a large hoop net that acts as a funnel to trap swimming fish.
‘Killed so pointlessly’
Six otters were found in the trap, some of which had been there so long only their skeletons remained.
Julia Stansfield, from the Environment Agency, said: “It made me so sad to see a beautiful, healthy animal like this killed so pointlessly.
“People sometimes complain about rules and regulations, but in this case there are very good reasons.”
Rupert Pyett, from the Environment Agency’s enforcement team, said of the illegal crayfish traps: “Ironically, if the people who had set these traps had contacted us, we could have told them they were wasting their time as there are no crayfish left in the Waveney.”
Killing otters, water voles and native crayfish can result in a fine of up to £5,000 or up to six months in prison.