The Krassach is a left tributary of the Weismain about 7 kilometers long, which flows into the Main near Altenkunstadt in Upper Franconia.

Just before reaching its mouth, it passes by the joint sewage treatment plant of Altenkunstadt and Weismain and is used as a freshwater supply.

[citation needed] The entire length of the Krassach River is flanked mainly by alder and willow trees.

They act as buffer strips between the river and adjacent agriculture, offering shade that helps keep the Krassach from warming.

Also, in its upper reaches, the Krassach has a lively alternation of feeder-rich, faster-flowing and shallower, slower-flowing sections of water.

[5] The Krassach River is a habitat for various species, including bullheads, brook lampreys, and brown trout.