- O Arco
- O cabalo, Bueu
- OAK-MOORE WRECK
- Oak Park
- Oakland Ridge
- Oasis
- Oasis, Tuticorin
- Oberoi House Reed
- Obersee
- Observatory
- Obyan
- Océanie
- Occhio di Dio
- Occhogahama
- Ocean Diver
- Ocean Diver Wreck
- Ocean Wind Tug (Wreck)
- Ocean’s Paradise
- Octopus Reef
- Octubre Rojo
- Odyssey Wreck
- Oedolgae
- Oeil
- Oesterputten
- Ofen
- Off Kadena Marine
- Office
- Ogan
- Oganzaki Lighthouse
- Ogi Port
- Oh My Bommie - Great Detached Reef - GBR
- Ohinau
- Ohoba No.1 Crevasse
- Oike
- Oil Rig Reef
- Oil Slick Leap (20)
- Oira
- Ojamo Mine
- Ojo de Agua
- OK Marine Pro
- Okikawa Maru
- Okinose W Arch
- Okinoshima Island
- Okirai Namiita Beach
- Okishima
- Oključna
- Okobe Thila
- Okorotere Island
- Oksuz Ada
- Okubo Hama
- Olang Sanctuary
- Old Aquarium
- Old Cement Barge
- Old Fort
- Old House Reef Makadi Bay
- Old Isaacs
- Old Jetty
- Old Man's Hat
- Old Pian Island
- Old Quarry
- Old Quarry Golf Course
- Old Virgin
- Old Wreck Head
- Olhuveli House Reef
- OLHUVELI HULANGU FARU
- OLHUVELI MEDHU FARU
- Oliveira e Carmo (Wreck)
- Olivetta
- Ollo do Mar
- Olnes Pond North
- Olo
- Olowalu Beach
- Olympia Maru
- Olympia Regattaanlage Oberschleißheim
- Olympia Regattaanlage Oberschleißheim (Süd)
- Olympia Regattastrecke
- Om Almaradem أم المرادم
- Om halhalla
- Oma Sukan
- Omi-Maiko Nakahama Beach
- Omijima Island
- Ondartxo
- Onderwater Natuurpark Zegersloot
- One Finger
- One Palm Finolhu
- One Rock
- One step beyond
- One Tree Bay
- Onna Point
- OOKOLHU FARU
- Oortkaaten
- Oosterschelde, Bergse Diepsluis
- Oostvoornse Meer
- Oostvoornse Meer Slag Baardmannetje
- Open Ocean Habitat
- Openluchtzwembad De Slenken
- Opera House
- Optisport zwembad Wolfslaar
- Orak Adası
- Orange Canyon
- Orange Cliff
- Orange Coral
- Orange Forest
- חוף אורנים, Oranim Beach, Ashdod
- Orca Housereef
- Orchard Beach (A/k/a Captain Mike's Beach)
- Organ Loft
- Orimas Thila
- Oriza Park Beach
- Orizaba
- Ormestad
- Oro Verde (Bow)
- Oro Verde (Wreck)
- Oros
- Ortello
- Orud
- Ory Faru
- Os Cairos
- Osaki Batfish Reef
- Osaki Hanagoi Reef
- Osaki Lion Fish Palace
- Osborn Shoals
- Osborne Shoals
- Osezaki
- Osezaki Beach
- Osprey
- Ostermade Pier
- Ostseebad
- Oswaldo’s Drop Off
- OTA Pool
- Otomi Beach
- Otter Cove
- Ottoman Anchor
- Oude Kademuur van Zierikzee
- Oude veersedijk Wolphaartsdijk
- Ouderkerkerplas
- Oued Yquem Wreck
- 青海島内湾 (Oumijima Naiwan)
- Outer Pinnacle
- Outer Rock
- Outhouse Beach
- Outpost
- Outside Crystal Cove
- Outside Edge, Aliwal Shoal
- Oval
- Over Heat
- Overhang 16-20Mts
- Overhead Rock
- Overheat Reef
- Overlook Park, Canyon Lake, Texas
- Owase
- Owens Reef
- Owhiro Bay
- Oyashirazu
- Oyster Bridge
- Oyster Reef
- Oyster Stacks
