Schemes such as this have been proposed, see the Swansea Tidal Lagoon [0]. The bottom line is that they are crazy expensive for the power they deliver and just

Schemes such as this have been proposed, see the Swansea Tidal Lagoon [0]. The bottom line is that they are crazy expensive for the power they deliver and just don't compete against other renewables. [0]https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay https://en.wikipedia.org/wiki/Tidal_Lagoon_Swansea_Bay