Ah, the return of Sunday Classics!
I heard this one on the radio last week. It is a fantastic, moving piece composed by Bedrich Smetana back in 1874. He called it a Symphonic Poem - and that's what it sounds like to me. Here is an excerpt from his program notes:
"The composition depicts the course of the river , beginning from its two small sources, one cold the other warm, the joining of both streams into one, then the flow of the Moldau through forests and across meadows, through the countryside where merry feasts are celebrated; water nymphs dance in the moonlight; on nearby rocks can be seen the outline of ruined castles, proudly soaring into the skies. The Mouldau swirls through the St. John Rapids and flows in a broad stream towards Prague. It passes Vysehrad [ where an ancient royal castle once stood ] , and finally the river disappears in the distance as it flows majestically into the Elbe. "