Off the coast of Scotland is a tidal generator. Recent news item
here.
On the south island of NZed is a lake with a tunnel that outflows into the west coast (Doubtful Sound) In the tunnel is a turbine. Since the lake is like 300 ft above sea level, the drop to sea level provided the potential for generation. The power station sends the power to an aluminum smelter. The lake use to outflow to a river, but they control that outflow now. Not really the same as tidal power as it is more akin to a hydropower station at a dam.
At
this link is a list of potential problems for tidal generators. No free lunch.