Beachgoers, watch out! Britain's seas could become a "jellyfish soup" this summer!
Scientists reckon the number of the slimy creatures is on the up.
The Marine Conservation Society thinks the rise is down to things like pollution, over-fishing and possibly even climate change.
It's asking for people to report any sightings of jellyfish. But people are advised to not touch them because they can sting.
A nuclear power station in Torness, Scotland, had to be shut down in June after jellyfish got into its cooling water system.
There's more information about the jellyfish survey on the Marine Conservation Society website (the BBC's not responsible for the content of external websites).