Due to the value of beaver-created wetlands, in most states it is illegal to disturb beaver dams or lodges without a permit. For example, in the state of Massachusetts any work in a wetland area is overseen by a local Conservation Agent/Commission. When beaver activity poses a threat to human health, safety or property, permits can be issued in MA within a matter of days by the local Health Agent and the town Conservation Agent. No state permits are needed. While these local permits allow for rapid resolution of the beaver-human conflict, great care is taken to ensure that the wetland resource area is altered as little as possible, just enough to resolve the conflict. This approach to permitting does a good job of balancing the need to promptly protect human interests, with the need to protect and maximize the wetlands in the state.
Regulations vary from state to state. Before altering any problematic beaver dam you should contact your state, county or local wetland officials to determine what the wetland protection laws and regulations are in your state.