What does an amber light indicate when passing through a lock?

An amber light when passing through a lock indicates that boaters should approach the lock under full control. This signal serves as a warning that the conditions in the lock may not be ideal for quick or reckless movements. It prompts boat operators to reduce speed and prepare for possible instructions or action once they reach the lock. Being under full control is crucial for ensuring safety, allowing the operator to react appropriately to any changes in the environment or directions given by lock personnel. It ensures that the boater can navigate safely and effectively, preventing accidents and ensuring the orderly movement of vessels through the lock system.

The other options do not convey the necessary caution and control that the amber light signifies. For example, proceeding at full speed does not align with safe practices in a confined space where other vessels may be present, and waiting for clearance is not directly related to what the amber light signifies in terms of approaching the lock. Unauthorized access does not relate to the amber light's meaning but could be indicated through different signals or protocols. Therefore, prioritizing control and careful navigation is essential when encountering an amber light at a lock.