In many wilderness areas, river floods are a common occurrence.

In spring, an enormous snowmelt can engorge the streams and rivers it feeds. Other catastrophic events such as massive rainstorms or the destruction of a dam can create floods as well.

During a flood, rivers become wider, deeper, and swifter. Assume that a river rises by 1d10+10 feet during the spring flood, and its width increases by a factor of 1d4×50%. Fords may disappear for days, bridges may be swept away, and even ferries might not be able to manage the crossing of a flooded river. A river in flood makes Swim checks one category harder (calm water becomes rough, and rough water becomes stormy). Rivers also become 50% swifter.