Kama (kä′ mȧ), the principal branch of the Volga, rises in the Russian province of Vyatka, and after an almost circular course of 1,000 miles joins the Volga about 40 miles below Kazan.  The Kama is navigable from Perm, a distance of over 900 miles.  It is free from ice a little more than half the year, and is one of the most important highways of commerce between Siberia and St. Petersburg.