The Summer Current is a warm sea current located on the south side of the Sea-known-as-Woden's-Bathtub in the Barbaric Archipelago. The Summer Current leads to Hysteria from the south, and Villainy from the north.
This current is distinguished by the constant presence of a bloodthirsty dragon species, known as Sharkworms. It seems that only Sharkworms are encountered here.
The young Hooligans that were part of the Pirate Training Program led by Gobber the Belch were sailing on the Sea-Known-as-Woden's-Bathtub. Hiccup and Fishlegs' ship, The Hopeful Puffin, was bumped into the Summer Current by Snotlout's and Dogsbreath's ship, Sparrowhawk.
Once in the current, the two boys encountered some Sharkworms and a Roman ship.