Down by Blackwaterside (also known as Blackwaterside, Blackwater Side and Black Waterside), (Roud 312, Laws O1 and Roud 564, Laws P18) are traditional folk songs, provenance and author unknown, although they are likely to have originated near the River Blackwater, Ulster.
The song tells the story of a woman who has her heart broken "down by Blackwaterside" when a suitor breaks his promise of marriage that he made to trick her into having sex with him. The morning after her suitor mocks her for believing that he would marry her and tells her to go back to her father. He tells her she has only herself to blame for having sex before marriage. She realizes he will never return and berates herself for believing his lies.
The Roud 564 variant of the song was popularized by a BBC Archive recording of an Irish Traveller, Mary Doran recorded by Peter Kennedy and Sean O'Boyle on either the 24th of July or the 1st of August 1952. During the same recording sessions her husband Paddy Doran and Winnie Ryan also performed versions of the song.
Mary Doran's version was taught to the singer Anne Briggs by A. L. Lloyd. Anne Briggs in turn taught it to singer/guitarist Bert Jansch. It appears on Jansch's 1966 album Jack Orion as Blackwaterside. Early in 1965, Briggs and Jansch were performing regularly together in folk clubs and spent most of the daytime at a friend's flat, collaborating on new songs and the development of complex guitar accompaniments for traditional songs. Anne Briggs has noted that "Everybody up to that point was accompanying traditional songs in a very [...] three-chord way. [...] It was why I always sang unaccompanied [...] but seeing Bert's freedom from chords, I suddenly realised—this chord stuff, you don't need it".Blackwaterside was one of the first songs that they worked on. Briggs belatedly recorded the song on her eponymous 1971 album (by which time she was playing a guitar accompaniment), though Jansch had recorded it 5 years earlier on his 1966 Jack Orion album. It is not known when Jansch started singing the song in the folk clubs, but certainly before the recording of Jack Orion. The story of Jansch learning the tune from Briggs is retold in Ralph McTell's "A Kiss in the Rain."