According to this source,

https://www.glcclub.com/h56-harbor-beach

Harbor Beach is one of the largest man-made harbors in the world! First built after the civil war as a harbor of refuge.

Huge boulders, line this massive breakwater which totals 1.8 miles in length, creating a 611 acre harbor (0.95 sq miles).

Great sunset tonight reflecting on this port’s entrance light.