Watch Victoria Davies' report.
This dolphin died off the coast of Cornwall after it became tangled in old fishing nets.
But sadly this is not an unusual sight.
Lost or abandoned fishing gear is regarded by conservationists as the most damaging plastic in our oceans, as it continues to fish long after it has been lost.
“Fishing nets are made of nylon which persist for hundreds of years in the marine environment if lost,” Matt Slater, from Cornwall Wildlife Trust, explained.
“It is really sad but a lot of reefs and wrecks around Cornwall are festooned with lost fishing nets and the amount of gear out there is pretty scary.”
It is estimated more than 640,000 tonnes of fishing gear is lost at sea every year.
‘It will continue to catch and kill’
But a group of divers in Falmouth are helping to turn the tide.
Members of charity Fathoms Free are giving up their free time to locate and remove what is known as “ghost nets” from the sea.
It only takes divers a few minutes to find an area covered in old fishing nets.
“This is a large piece of monofilament net,” Natallia Paliakova says.
“You can see it looks like it has spent a bit of time down there because it has a little bit of growth on it and it is slightly discoloured, but essentially it's not damaged.
Elsewhere in Cornwall, members of British Divers Marine Life Rescue are regularly called to help seals who are seriously injured by old fishing nets or rope.
Cornwall has one of the largest seal entanglement rates in the world.
“I have got an example here of a piece of net that we took off a seal a couple of years ago here in Cornwall,” Dan Jarvis said.
“It doesn't look like very much but it is enough to kill. If it gets caught around their neck, they cannot get it off unfortunately and it leaves these really horrendous injuries.
“It is tough material, it is designed to last so it is really difficult to break and this sort of material can last hundreds of years in the environment and kill many animals in its lifetime.”
Having saved many seals, Dan said people need to start picking up any old net they see washed up on the beach.
“Hand on heart, you could save a life by doing that,” he added.