A tidal harness can be constructed by terraforming units and can allows energy collection in an ocean square. Squares with tidal harnesses produce +3 energy per turn.
Tidal harnesses can only be built in ocean shelf squares (depth less than 1000m). With the discovery of Adv. Ecological Engineering, aquatic factions such as the Nautilus Pirates can also construct tidal harnesses on ocean and ocean trench squares.