Complex sentence: The river formerly provided motive power for tanneries and mills, but its flow is now somewhat reduced by the Lac de Pont, a dam built upstream in the 19th century to provide water for the Canal de Bourgogne.
Split into simpler sentences: The river formerly provided motive power for tanneries and mills, but its flow is now somewhat reduced by the Lac de Pont. The dam was built upstream in the 19th century to provide water for the Canal de Bourgogne.