The Great Summer Lake is a quite large lake in southern Koth (top left of the bottom right map of Pendria).
It stays quite warm, probably due to underground heat from a shallow magma pool or the like.
Many fish can be caught in the waters of the lake, mostly trout, bass and catfish. It is not unknown for rarer fish types, such as Sagefish or Mithril trout, but they are quite rare and expensive, usually coming up for auction when caught.