Marine scientists were visited by a pod of about 20 dolphins off the Cornish coast.
Plymouth Marine Laboratory (PML) said maintenance was being carried out on a data buoy about four miles south of Rame Head when the dolphins arrived.
Bio-optical oceanographer Dr James Fishwick filmed the "surprise visit".
The pod swam around the buoy and played in the water for about 30 minutes allowing Dr Fishwick to take several close-up photographs.
PML said despite an increase in common dolphins over recent years, close encounters of this type were still infrequent and the scientists were thrilled by the experience.
"I have spent years working out here, off the coast of Plymouth, and even though I knew dolphins can be seen in these waters, I have never been privileged enough to spot one, let alone 20, before," Dr Fishwick said.
He said the experience was a visual reminder of how important marine research was.
"Although our research often focuses on the chemistry and biology of the oceans and important smaller organisms within it, these help to sustain the larger animals, such as whales and dolphins," Dr Fishwick said.
"It is therefore important to understand how changes in the marine environment will affect oceanic processes and the organisms at the base of the food web, to appreciate the impacts upon larger animals."
Dr Fishwick is part of a group of scientists working on the Western Channel Observatory project, which is hosted at PML.
The group measures a range of physical and biogeochemical conditions in the channel which provides important information for scientists, the UK Met Office, the fishing industry, sailors and divers.