This little sleeping Sjörå - or Keeper of the Lake - seems to be the reason for the Instagram madness. You can see the post here.
A sjörå is a female water creature in Scandinavian folklore.
"Sjö" means lake. "Rå" is a mythological being that is a keeper or warden of a particular location, such as lakes, forests or mountains.
She is a shapeshifter and can take the form of a full grown human-like being, as well as a small fish-like creature - as you can see here her colours and markings are much like an abborre (perch).
If you go fishing, you should be careful not to encounter a sjörå. Although, by sharing your picnic with her, she might grant you with a great fishing luck.