If you can access the dam, go over there and start ripping it apart. Mess it up enough to increase water flow through it. The beavers will know something is up with the dam and come to check it out. We used this tactic many times at my parents place and others and it works great. They come swimming in and I had live target practice with my deer rifle! A 30.06 and .270 do a number to the head of a beaver Even if your property is not by the dam, you may catch them coming by your place to check it out.