Maria Sanchez Lake, in St. Augustine, was created back in the 1800s, when Henry Flagler filled in the upper reaches of Maria Sanchez Creek, and built hotels on the resulting land. A dam was built at South street, causing the creek to spread. Over the decades the little tidal lake has developed an ecosystem, providing food for several bird species. It's all about to become history, what little natural vegetation exists will be killed by the concrete seawall, the ecosystem will fail, and the birds will go away.
I can't imagine any rational motive for building this eyesore, any erosion could be controlled at less expense, and with far less damage to the ecosystem, and the human eye!