Which operations must be conducted on a restricted sector of the waterway?

Conducting military operations is the correct answer because restricted sectors of a waterway are specifically designated for activities that require heightened security and control, such as military exercises. These areas are often marked to prevent unauthorized access and ensure safety during operations that may involve live-fire exercises, troop movements, or other sensitive activities that could pose a risk to civilians or other vessels in the area.

In contrast, recreational boating, commercial fishing, and environmental research typically do not require the same level of security or restricted access. These activities are generally carried out in open or designated areas where the risks are managed through established guidelines and safety protocols, rather than through restricted operational zones. Therefore, it is essential to recognize the unique requirements and safety considerations associated with each of these activities when determining appropriate operations within restricted sectors.