The refrain of Sweet Thames, for interest, comes from Prothalamion; or, A Spousall Verse in Honour of the Double Marriage of Ladie Elizabeth and Ladie Katherine Somerset, a poem by Edmund Spenser (1552-1599), one of the most important poets of the Tudor Period in England.
He tells of walking by the Thames and following two beautiful swans up the stream to London, where they meet and marry two fine young men. Each stanza ends with the refrain

"Sweet Thames, run softly till I end my song."

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