How can tides be harnessed?

Question

How can tides be harnessed?

Answer 1

there is a kind of underwater windmill that can be used for this purpose. tidal water flows with great force through canyons in cliffs near the sea in some parts of the world and this could be harnessed. extracting power from the tides will slow the moon very very slightly,

Answer 2

There must be hundreds of designs to do this but very little energy can be gained from tides. They have some tidal power in Holand or at least have plans for such.