The beaver species seen in North America is the American beaver (Castor canadensis). Its European counterpart, Eurasian beaver (Castor fiber) is slightly smaller, but plays a similar environmental role.
The North American beaver population was once more than 60 million, but the species was trapped virtually to extinction in the 1800s for beaver pelts. In recent decades, decline in demand and proper wildlife management has allowed beavers to become re-established in much of their former range.
Photo courtesy of WDFW