Project Mermaids model. Project Mermaids lets ocean-lovers don tails and live out their siren fantasies. Clients can pay for a shoot that is either on land or underwater, with the images looking to raise awareness about preservation of beaches, seas and oceans. The project – which is shot by photographers Angelina Venturella and Chiara Salomoni – started purely to raise awareness, with celebrities dressing up as sirens as part of the cause. (Photo by Angelina Venturella/Chiara Salomoni/Caters News Agency)

Teeming with images of spectacular underwater scenes from around the world, Call of the Blue is the culmination of a five-year project by the photographer and ocean conservationist Philip Hamilton. This groundbreaking book includes contributions from acclaimed scientists and ocean “guardians”, who reveal what drove them to answer the call of the blue. (Photo by Philip Hamilton/The Guardian)

These photographs appear to show a spectacular underwater world making it ideal for scuba divers – in central Europe. Twelve metres of water covers trees, footpaths, benches and bridges that are usually accessible throughout the year. Visitors to the Green Lake in Tragoess, Austria, that is normally only one metre deep, can leisurely stroll around the picturesque lagoon. Photo: A diver crossing a bridge in the flood water. (Photo by Solnet/The Grosby Group)

Charli XCX arrives for the 30th Annual ARIA Awards 2016 at The Star on November 23, 2016 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)

Luke Timms of Australia poses during the pre judging of the IFBB Australian Pro Grand Prix XI at Plenary Hall on March 12, 2011 in Melbourne, Australia.

Underwater photographer Alexander Semenovs has snapped some of the most stunning, fragile life forms anywhere on planet Earth. Shot in deep, dark conditions, the images continue to provide an insight into what lies beneath, with glowing creatures appearing a lot like aliens in the pitch-black water. Semenovs has shot the likes of bioluminescent jellyfish, aggressive-looking worms and many species that leave a lot to the imagination. The 30-year-old from Moscow does the majority of his work in the White Sea, near the Arctic Circle. Here: A Comb jelly – Beroe cucumis. (Photo by Alexander Semenovs/Caters News)

The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21 as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, located 62 feet below the surface of the Atlantic Ocean in the Florida Keys National Marine Sanctuary. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. During simulated spacewalks carried out underwater, they will evaluate tools and mission operation techniques that could be used in future space missions, including journeys to Mars. (Photo by Karl Shreeves/NASA)

A man watches a wave hit a rock pool at Curl Curl beach as large swell hits the East Coast of Australia on June 6, 2016 in Sydney, Australia. Torrential rain over the weekend saw streets and homes flooded while wind gusts up to 120km per hour brought down trees and powerlines. A king tide has also seen beachside homes evacuated on Sydney's northern beaches as large waves erode the coast. (Photo by Cameron Spencer/Getty Images)