On Wednesday, the Brighton BSAC '007' SCUBA Diving Club were returning from a dive when they saw the pod of bottlenose dolphins.
According to the group, at least 30 of the mammals were seen travelling east to west.
Dan McLaughlan from Burgess Hill was on the boat. He described the sight as 'pretty special'.
The video was posed on the group's Facebook page, with a quote which said: "You never know what you're going to see under the water or above!"
If you would like to join the diving group, search Brighton BSAC '007' SCUBA Diving Club on Facebook.