Sergio Hanquet / Green turtle (Chelonia mydas) heading towards surface to breathe beside boat. Collision with boats and propellers poses a danger to turtles. Tenerife, Canary Islands.

Sergio Hanquet / Green turtle (Chelonia mydas) swimming in proximity to boat propeller; propellers are a danger to sea turtles. Tenerife, Canary Islands.

David Fleetham / Florida manatee (Trichechus manatus latirostris) showing healed wounds from contact with a boats propellers, Three Sisters Spring, Crystal River, Florida, USA.

David Fleetham / Diver swimming behind the propeller of the wreck of the Hilma Hooker, a 236 foot long cargo vessel that sunk in 1984 off the island of Bonaire in the Caribbean.

Tony Wu / Southern right whale (Eubalaena australis) fluke marked by injuries that appear to be the result of a propellor strike from a boat traveling at high speed, photographed with the permission of the Depa...

Pascal Kobeh / A diver on the wreck of the Bristol Blenheim bomber shot and which crashed in December 1941, Malta, Mediterranean

Pascal Kobeh / A diver on the wreck of the Bristol Blenheim bomber shot down in December 1941, Malta, Mediterranean

Franco Banfi / Yellow sponges (Aplysina cavernicola) on propeller pt the wreck 'Vassilios T', Vis Island, Croatia, Adriatic Sea, Mediterranean

Michael Pitts / Diver on the wreck of the Italian cargo ship 'Umbria' looking at the Starboard propellor, scuttled in Port Sudan 10th June 1940, Red Sea, March 2008

Benoit Stichelbaut / Man working on propeller of fishing trawler "Jack Abry II" in Concarneau dry dock, Brittany, France. June 2007.

Benoit Stichelbaut / Man working on propeller of fishing trawler "Jack Abry II" in Concarneau dry dock, Brittany, France. June 2007.

Benoit Stichelbaut / Shipyard workers cleaning a fishing boat on the slipway at Concarneau, Brittany, France.