Composed for the birthday (October 7, 1733) of August III, elector of Saxony and king of Poland, Bach's Cantata No. 206 "Schleicht, spielende Wellen, und murmelt gelinde" (Glide, playful waves and murmur gently) (BWV 206) was not actually completed until 1736, having been delayed by war and other commissions. The cantata is one of Bach's largest vocal works, consisting of 11 substantial movements and lasting 40 minutes in performance. The cantata is scored for bass, tenor, alto, and soprano soloists and chorus, three flutes, two oboes, three trumpets, tympani, strings, and a basso continuo consisting of lute, harpsichord, cello, and double bass. It is the conceit of the anonymous text that each of the four soloists is the embodiment of each of the four principal rivers of Poland: the Pleisse (soprano), the Danube (alto), the Elbe (tenor), and the Vistual (bass).

The work opens with a massive, celebratory choral fantasia for chorus and full orchestra. This is followed by pairs of secco recitatives for each of the four soloists rising from the bass to the soprano. The third-movement bass aria is scored for strings and continuo. The fifth-movement tenor aria is in the form of a trio sonata with violin obbligato. The seventh-movement alto aria is a quick dance movement in the form of a trio sonata with both oboes obbligato. The ninth-movement soprano aria is accompanied by the three sweet flutes. The tenth movement is a recitative for all four soloists plus strings and continuo. The cantata concludes with a triple-time choral hymn of praise for August III.

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