Portal:Rivers/Did you know/3

Maksimovsky rock in the Chusovaya River in Russia

... that a tributary of the Chusovaya River (pictured) naturally dives underground for about 6 kilometres (3.7 mi)?
... that the Cheddar Yeo forms the largest underground river system in Britain?
... that the "Mad Raft Race" is an event held on the Chilkoot River as part of Fourth of July festivities observed in Haines, Alaska?