River Euphenics is the first river introduced in Shintolin and was the longest one before the discovery of River Dea. Previously known as River Iis (named after the game's creator, Isaac) the name of the river was changed to its current form to honor Euphenics, a great player in both Shintolin and Shartak - indeed, as he began the very first settlement, he could be called the founder of civilisation in Shintolin. The river has an unnamed tributary river starting from the hill south of Deadwood.

The river's source is situated in The Feral Hills, on top of one of the highest hills in the world (where Tonkytown once prospered). From there it flows directly south until it reaches Vackra Alskade from where it starts to form curves. However, due to its size, there aren't any floodplains on the banks of River Euphenics when it is snakes through The Midlands. After it has weaved a couple of times it flows into Hermit Lake in the vicinity of Citrus Hill.