Which of the following is not a category used to classify wrecks?

In the classification of wrecks, "natural" does not fit into the established categories. Wrecks are typically classified based on their origin, condition, and significance. The primary categories include artificial wrecks, which are intentionally sunk structures—such as reefs or ships designed for diving—as well as contemporary wrecks, which refer to more recent sinkings that have occurred in modern times. Historic wrecks are those that have significance due to their age or historical context.

Natural formations, on the other hand, do not relate to the concept of wrecks since they are not the result of human activities—such as the ship sinking or crashing. Understanding the categories is crucial for divers as they plan dives, assess conditions, and aim for preservation and safety in those environments.