Organisers of this year's National Whale and Dolphin Watch say Welsh coasts recorded some of the best sightings.
The event, hosted by the marine research and conservation charity Sea Watch Foundation, recorded more then 415 sightings around the UK.
In Wales, harbour porpoise and bottlenose dolphins were widely reported.
Risso's dolphins were recorded off Grassholm and Skomer in Pembrokeshire and West of Holyhead Breakwater, off Anglesey.
The video shows some fantastic footage of dolphins flipping jellyfish out of the sea and into the air. It was recorded a few years ago off Tremadog Bay. Dolphins also eat some types of jellyfish so they will be welcoming the rise in supplies!
A group of jellyfish is called a bloom or swarm. They do not have a brain or central nervous system but a network of nerves.
Jellyfish are made up of more than 90% water and are fragile.
The lion’s mane jellyfish is the largest known species of jellyfish and they have a sting. Some have been spotted at Benllech beach on the Menai Strait according to the Marine Conservation Society. If you do get stung apply vinegar!