In lakes, rivers and large streams with deep enough water, beavers may not build dams and instead live in bank burrows and lodges. If the water is not deep enough to keep beavers safe from predators and their lodge entrances ice-free, beavers build dams. ... The thickness of the dam is often around 1 m or more.
Beavers have been known to be extremely aggressive in defending their territory against perceived encroachment. They may attack humans when suffering from rabies, and "can also become disoriented during the daytime and attack out of fear". ... Beaver attacks can also be fatal for domestic animals.