I was across the bank for the video, about 15' away. I was closer for the photos. What's interesting is actually how aware they are of the human presence; I think it's more that he just wasn't threatened by us. The beavers always noticed people before people notice the beavers (same is true for domestic dogs). The beavers' response was variable from person to person, the most dramatic response is a tail slap when the person is still about 100yds away, for others they'll simply slip into the water and swim up or downstream.