The longest beaver dam found with Google Earth to date (October 2, 2007) is located in Northern Alberta. The dam has a length of about 850 meters (2790 ft). It has at least existed at this spot for over 25 years as it can be observed on the 1990 Landsat 7 Pseudo Color Imagery provided by NASA World Wind.

Parrr Geng
Source: EcoInformatics