wave fappers I've heard about tidal generators in Maine that the tides were running so strong that not only was it strong enough to produce a crap load of energy, it ripped the 20 ton generator off the inlet bottom . And the other design is the wave flapper, at unsurfable coasts there are hinged flaps the use magnetic friction generators to use the waves motion to create energy. No fish kill there, But im not sure about the efficiency of that method