Why must vessels navigate with extreme caution under certain conditions?

Navigating with extreme caution under certain conditions is essential primarily to prevent collisions and ensure safe passage on the water. Various factors, such as reduced visibility due to fog, heavy rain, or darkness, can significantly impair a navigator's ability to see other vessels or obstacles. In such situations, the risk of collision increases, making it crucial for vessels to exercise heightened caution and adhere to the rules set forth in the COLREGs.

This means not only staying vigilant and keeping a proper lookout, but also adjusting speed, using sound signals, and ensuring that appropriate maneuvers are made well in advance to avoid potential hazards. The emphasis on situational awareness and safety underlines the responsibility vessels have to avoid incidents that could lead to collisions, protecting both crew and cargo, as well as the environment.

The other options, while they may hold some relevance in certain contexts, do not address the primary concern of navigating cautiously to ensure safety from collisions, which is the core objective of the COLREGs.