The document discusses tidal fence turbines, which are devices used to harvest kinetic energy from tidal currents. Tidal fence turbines are entwined together like a fence and submerged in sea areas with strong tidal currents. They work by having vertical turbine shafts that spin due to tidal currents, which then turn attached generators to produce electricity. Existing tidal fence turbines are located in areas like the UK, Scotland, Canada, South Korea, and France. The document outlines some advantages like predictable energy production and being clean energy, as well as disadvantages such as high initial costs and potential environmental impacts.