Specialist wildlife crime officers are investigating the death of a bottlenose dolphin which is believed to have been killed by a boat.
The calf was part of a pod of the rare dolphins which entered the Camel Estuary at Padstow in Cornwall at around 1.30pm on Saturday.
A flotilla of 25 pleasure boats followed the dolphins - with some circling the creatures - until they left the estuary at around 4.45pm and headed up towards Port Quinn Bay.
When the pod left, the body of the calf was spotted in the water. It was found at The Rumps, north east of Pentire Point, which is between Polzeath and Port Quin.
Officers believe the dolphin was hit by one of the boats and are appealing for witnesses to come forward.
Marine campaigners Sea Shepherd UK and Dive Master Insurance have put up a £2,000 reward for information leading to the conviction of the person or people responsible.
Pc Del Allerton-Baldwin, wildlife crime officer on the Marine and Coastal Policing Team in Bodmin for Devon and Cornwall Police, said: "We would like to get a list of all boats that were in the area at the time. They should all have names on them.
"Many of the boat users were in fact behaving responsibly around the dolphins and keeping a distance of around 100 yards. However a few appear to have been harassing them.
"If you were part of the flotilla, it does not mean you were committing an offence but we would like to speak to you and eliminate you from our inquiries. You may also have vital information which may assist with the investigation."
The force would like any photographs or videos of the flotilla of 25 boats in the area between 1.30pm and 5pm on Saturday.
In a joint statement, the British Divers Marine Life Rescue and the Cornwall Wildlife Trust accused the boats of "harassing" the dolphins.
It said: "Boats started to congregate at the area where the group of bottlenose dolphins were first spotted. Many boat users acted responsibly and observed the animals from a distance. Shortly after this picture was taken, a number of speeding boats crossed over the pod and between the boats.
"Very soon after, a carcass was reported to have been found at the scene. The death is believed to be as a result of the harassment.
"This photo is of a juvenile bottlenose dolphin that is believed to have been killed as a result of the incident. It was taken by the crew of a Padstow sightseeing vessel. When they first spotted the dolphin there was signs of blood in the water around the animal, as if recently struck.
"This photograph was taken later when the crew unsuccessfully attempted to recover the body but took pictures for reference."
Harassing dolphins is a crime under the Wildlife and Countryside Act 1981, with conviction carrying a maximum sentence of £5,000 and/or six months in prison.
Inshore bottlenose dolphins are nationally rare and losing just one could threaten the population, according to the Cornwall Wildlife Trust.
It has not been possible to recover the carcass of the calf and anyone who finds it is asked to contact the Cornwall Wildlife Trust Marine Strandings Network.