A vessel showing a green light over a white light in a vertical line above the level of the sidelights is

• A. Fishing near a fishing area
• B. Not under command
• C. Trawling
• D. Sailing vessel in sight of land

Answer: (C)

Vessels that are actively fishing use special lights to signal their status to other ships. When you see a green light arranged above a white light in a vertical line, and this signal sits higher than the vessel’s sidelights, that identifies a fishing vessel engaged in trawling. The gear being dragged can extend far to the sides, so this signal alerts nearby vessels to exercise caution and keep clear.

This is why the best interpretation is that the vessel is trawling. Other possibilities like not under command or sailing near land don’t match this light pattern, and the signal is specifically used to indicate fishing operations, with trawling being a common form. In practice, you should slow down, keep a safe distance, and pass with care to avoid entanglement with gear.