The ear jellyfish, as the species is called, are in a so-called medusa stage that occurs when they become sexually mature and reproduce. What the boom is due to is a little unclear, but the fishery maintains that favorable conditions and the right winds can bring large quantities to the coasts.

This is what it looks like under the jetties in the Stockholm archipelago - full of jellyfish Photo: Stockholm city fishery

Robin Malmsten Havervall has been down below himself

Robin Malmsten Havervall has dived in many places around the world, comparing the natural phenomenon with what one can witness during the popular diving destination Jellyfisk Lake in Palau, outside Indonesia.

Jellyfish have been collected in the Stockholm archipelago Photo: @travel_ons / Robin Malmsten Havervall

- The jellyfish was everywhere, even when we took the ferry from the mainland we saw the jellyfish from the boat. But it is impossible to see how many they actually are until you are below the surface. Then it is incredibly cool. They are a little pinkish so it looks very nice too, says Robin Malmsten Havervall.

What tips do you have for those who want to see the jellyfish?

- Those who want to experience this should put on a thick wetsuit because it is quite cold in the water, around eleven degrees. Then it is just to go out to some archipelago island, says Robin Malmsten Havervall.

Jellyfish have been collected in the Stockholm archipelago Photo: @travel_ons / Robin Malmsten Havervall

The jellyfish have also become a concern for the local fishermen in the archipelago. According to Stockholm City Fisheries, fishermen complain that it is impossible to put out nets when the jellyfish are so many in number.