Construction of a small dam near the far end of a bay, harbor, lagoon, fjord, estuary, or coastal waterway gravitationally connected to the ocean, creating a small artificial tidal basin that becomes sealed off from the ocean, except for a small opening in the dam.  Placement of a reversible hydroelectric generator in the opening of the dam to generate electricity from the flow of water through the dam -- into the basin on the rising tide and out of the basin on the falling tide.  The tidal basins must be constructed at locations that will not disturb natural fish or sea life habitats.  The generators must be screened from the ocean to prevent fish, seaweed, and other solid matter from entering the generators.  The screens must be cleaned frequently (preferably by energy-efficient automatic scrubbers). 

In some settings, multiple generators in a single dam may be the most efficient arrangement.

At locations where boats pass between the tidal basin and the open sea, gates in the dam can be constructed so that they can be opened during the hours straddling low and high tides, when ocean level changes are minimal.  The gates do not have to be water-tight.  Small leaks through the gates will not materially affect the energy generation of the facility.