Up until 1998 killing or injuring a swan was classed as treason, under an ancient law dating back to the 12th century. The Crown retains the right to ownership of all unmarked mute swans in certain stretches of the River Thames, which means killing or injuring a swan can be classed as criminal damage. It is also an offence to injure, take or kill a wild swan as they are protected under the Wildlife and Countryside Act 1981.