The correct answer is C) Western Rivers. According to the regulations, towing vessels over 39.4 feet in length are not required to carry an echo-sounding device when operating on the Western Rivers. This is because the Western Rivers are relatively shallow and the navigational hazards are generally well-known, making an echo-sounder less necessary for safe operation. In contrast, towing vessels on Inland Waters (other than the Western Rivers), Coastwise Routes, and the Great Lakes are required to carry an echo-sounding device, as these waterways may have deeper, less familiar depths and submerged hazards that require more precise depth information for safe navigation.