The River Moss is a large river which runs from the east, flows through Mossflower Woods, meanders north of Redwall Abbey, fords the Northern Path, and empties into the Western Sea. The river sometimes constitutes a point of entry into Mossflower when boats are rowed with oars and pulled with ropes. This river has many tributaries and is populated by Guosim shrews and otters.
In the times of Tsarmina Greeneyes, the river was also populated by a gigantic pike fish named Stormfin kept by otters of the Corim. Martin the Warrior and the otters used Wuddship to dam the river, which led to the flooding of Kotir.
Interestingly, the River Moss has only been mentioned by name in the text of four books: Mossflower, The Bellmaker, High Rhulain and Eulalia!, though in the Redwall Map & Riddler and on the maps of Mariel of Redwall and Salamandastron it is labeled as such.