On Wikipedia
A harbor or harbour (see spelling differences), or haven, is a place where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use. Harbors can be natural or artificial. An artificial harbor has deliberately-constructed breakwaters, sea walls, or jettys, or otherwise, they could have been constructed by dredging, and these require maintenance by further periodic dredging. An example of the former kind is at Long Beach Harbor, California, and an example of the latter kind is San Diego Harbor, California, which was, under natural conditions, too shallow for modern merchant ships and warships.

What is the difference between a harbour and a port ?

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