Exactly. A coastline is probably the most volatile and inhospitable location for an underwater colony of any sort. Frankly, to get an even remotely stable under

Exactly. A coastline is probably the most volatile and inhospitable location for an underwater colony of any sort. Frankly, to get an even remotely stable underwater city in place, you'd need to do it fairly deep in the open ocean -- far beneath surface turmoil and major currents. Of course, this would pose its own nigh-insurmountable problems, such as ease of transportation into and out of the colony, pressurization, expense of maintenance, expense of supply routes, self-sustainability, and so forth. Underwater habitation is a lot further off than people seem to think it is.