Final answer:
Vessels must have a navigation light system on board when operating on inland waters between sunset and sunrise for safety and visibility.
Step-by-step explanation:
On inland waters, vessels must have on board a navigation light system when operating between sunset and sunrise. These navigation lights are essential for the safety of all vessels on the water as they help to prevent collisions by ensuring that a vessel can be seen by others and that the type and direction of the vessel can be ascertained. The navigation light system typically includes a red light on the port (left) side, a green light on the starboard (right) side, and a white light that is visible from all directions on the stern (rear).