Peter Rowlands, chair of the Underwater Photographer of the Year 2017, jury said: "From my own point of view, I have been captivated not only by the winning images but also by the stories behind how those images were achieved.
"The conception, the planning and the physical effort to achieve a successful result; it is those efforts that we, as judges, pay our respects to by taking out two days to meet up, sit together and look in detail at all the images. It is a mammoth task but one that we all agree is a privilege to be part of."
Gabriel Barathieu, of France, won Underwater Photographer of the Year, for "Dancing Octopus".
Juror Alex Mustard said: "Both balletic and malevolent, this image shows that the octopus means business as it hunts in a shallow lagoon. The way it moves is so different from any predator on land, this truly could be an alien from another world. A truly memorable creature, beautifully photographed.
Rowlands said: "Vibrant contrasting colours, detailed delicate textures and a perfect pose. Add the right choice of lens for the situation and they all combine to produce a champion."
Juror Martin Edge: "I cannot praise this photograph enough. As soon as I first set eyes on it as we worked our way through the Wide Angle Cat, I knew it was destined for a huge success. One amazing Image!"
Nick Blake was named British Underwater Photographer of the Year for "Out of the Blue".
Edge said: "What I really like about this image is the enclosure of the light within the Cenote. The author has contained all the sunlight so the eye of the viewer cannot escape. The lone diver is positioned within the beams and I do believe that the author meant for this to happen. Stunning natural light wide angle!"
The Wide Angle winner was American Ron Watkins for "One in a Million".
Watkins said: "Last summer I headed to Alaska in search of salmon sharks. We cruised in the boat looking for their dorsal fins for hours and that is when we came across an enormous moon jellyfish bloom that stretched for several hundred metres.
"The dense bloom of jellyfish ranged in depth from 2 metres to over 20 metres and we spent a lot of time in the water with them. It was surreal and more dense than anything I had ever experienced including Jellyfish Lake in Palau. I came across this lion's mane jellyfish rising from the bloom towards the surface and positioned myself directly over it to capture this image."
Mustard said: "A beautiful and original image from the ocean, a worthy winner. Its power comes from the contrast in colour, yellow versus blue, and the contrast in shape, star versus circles, between the subject from the background.
"Most photographers would swim up to the subject, probably shooting it from below, Ron found a far more striking composition with this top-down view, making use of the moon jellies as a background."
The Underwater Photographer of the Year 2017 exhibition is being held at the Chavonnes Battery museum at the Waterfront.