There are several designs of "beaver deceivers", and they work very well. I had chronic problems with beavers trying to plug up the in take to the fish farm until I put one in. Worked for years without trouble.
Google "Clemson Beaver Pond Leveler". You can make them out of PVC pipe. If the beavers aren't dead, removing the dam is just exercise and there is a high probability that another pair will move in next spring.