When is a vessel permitted to enter a separation zone?

A vessel is permitted to enter a separation zone to avoid immediate danger or to engage in fishing, as this aligns with the purpose and regulations established under the COLREGs. The separation zone is designed to keep different marine traffic streams apart, typically for the safety and efficiency of navigation. However, situations may arise where a vessel finds itself in immediate danger, and entering the separation zone is the necessary course of action to prevent a collision or other hazardous situations.

Additionally, engaging in fishing activities in a separation zone is permitted under specific conditions, although it should be approached with caution to ensure compliance with safety regulations. This highlights the flexibility within the rules when it comes to ensuring vessel safety and responding to emergencies.

The other options either impose unnecessary restrictions or suggest scenarios that are not permitted under the COLREGs. For instance, entering the separation zone only during daylight hours or specifically for overtaking another vessel does not align with the regulations, as the intent behind the creation of these zones is to maintain safe traffic flows, not to dictate the timing or specific maneuvering of vessels under normal circumstances.