This is one of many Songs without Words (or "Lieder ohne Worte") composed by Felix Mendelssohn. The "Songs without Words" were a popular form of expression for Mendelssohn, and in total he published 48 of these piano pieces in 8 sets of 6 spread throughout his tragically short life as a composer. The song titles were added later by publishers rather than by the composer himself, and the last song in each of the first two groups of 6 are both entitled Venetian Boat Song. This piece is the first "Venetian Boat Song" Op.19 No.6. The video below illustrates this piece with a piano roll animation, while below the video you can play the mp3 file and see the music before downloading.