In inland waters, if a vessel is displaying yellow over yellow lights, what is it doing?

When a vessel is displaying yellow over yellow lights in inland waters, it signifies that the vessel is pushing ahead. This configuration of lights is a standardized visual signal indicating the vessel’s intention and operational status. In this case, two yellow lights stacked vertically tell other vessels that the vessel is primarily engaged in a pushing operation, typically associated with towboats or barges that are moving ahead while pushing against another vessel or barge.

Understanding this signaling is crucial for navigational safety, as it allows other vessels to recognize the operational status of the pushing vessel and respond appropriately in order to maintain safe distances and avoid potential collisions. In contrast, the lights for anchoring, fishing, or towing convey different meanings and are configured differently, allowing for clear communication of a vessel's activities on the water.