beaver dams

The typical beaver dam is about 10 to 100 meters long. Many are only a meter high and few approach 3 meters.

The largest known beaver dam is in Wood Buffalo National Park in Northern Alberta. It is about 800 meters long. Google satellite image this link goes to another website It was discovered in 2007 by Jean Thie while using satellite imagery to investigate permafrost.

A dam in Three Forks in Montana previously held the record, at 652 meters. This may be that beaver dam.