current turbines have no environmental impact except visual, but very limited.
propellers rotate very slowly (between 20 et 50 t/min) so they do not damage
the submarine flora and fauna.
lot of tests and experiences carried out in various sites, rivers, seas, estuaries
have never shown any impact on the environment.
the contrary some fish species come and play during hours with the turbine,
but they never touch and get never touched by the propeller!