What lights must be shown at night on a moored barge that reduces navigable channel width to less than 80 meters?

The appropriate lights for a moored barge that reduces the navigable width of a channel to less than 80 meters are two all-round white lights. These lights are necessary to ensure that other vessels are aware of the barge's presence, particularly in low visibility conditions at night.

The use of two all-round white lights indicates that the barge is moored and helps other vessels gauge the restriction in the navigable channel. This is crucial for safe navigation, as it provides important visual cues to passing ships regarding the position and extent of the moored barge.

In contrast, the other options do not meet the regulatory requirements for visibility and identification of a moored vessel. For example, red lights typically indicate a danger or a moored vessel, but two all-round red lights are not specifically designated for a moored barge. Similarly, a single all-round green light typically indicates a sailing vessel engaged in fishing or other specific operational conditions, and would not serve the purpose for a moored barge. Lastly, the combination of one white light over one red light does not provide the necessary indication that would make a moored barge clearly visible and correctly identified at night.