| Creature | Terrain | Climate | Campaign | Reference |
|---|---|---|---|---|
| Afanc | Water, Ocean | Temp/Trop | Any | MAI |
| Afanc, Young | Water, Ocean | Temp/Trop | Any | MAI |
| Beholder-kin, Eye of the Deep | Water, Ocean | Any | Any | MM 21 |
| Bowlyn | Water, Ocean | Any | Ravenloft | RV 13 |
| Devilfish | Water, Ocean | Any | Any | DRC 165 |
| Dinosaur, Archelon | Water, Ocean | Any | Any | MAII 40 |
| Dinosaur, Dinichthys | Water, Ocean | Any | Any | MAII 40 |
| Dinosaur, Elasmosaurus | Water, Ocean | Any | Any | MM 54 |
| Dinosaur, Plesiosaurus | Water, Ocean | Any | Any | MAII 41 |
| Dinosaur, Temnodontosaurus | Water, Ocean | Any | Any | MAII 41 |
| Dinosaur, Tennodontosaurus | Water, Ocean | Any | Any | OMII 55 |
| Dragon, Amphi | Water, Ocean | Temp/SubTrop | Dragonlance | DLMC |
| Dragon, Brine | Water, Ocean | Any | Any | MAII 44 |
| Dragon, Linnorm, Midgard | Water, Ocean | Any | Any | MAI |
| Dragon, Oriental, Lung Wang (Sea) | Water, Ocean | Temp/Trop | Forgotten Realms | FR1MC |
| Dragon, Oriental, Tun Mi Lung (Typhoon) | Water, Ocean | Temp/Trop | Forgotten Realms | FR1MC |
| Dragon, Sea | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Dragon-kin, Sea Wyrm | Water, Ocean | Sub-Trop/Trop | Any | MAII 46 |
| Elf, Sea, Dargonesti (Deep) | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Elf, Sea, Dimernesti (Shoal) | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Ghaggler | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Ghaggler, Champion | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Ghaggler, Warrior | Water, Ocean | Temp/Trop | Dragonlance | DLMC |
| Giant, Reef | Water, Ocean | Sub-Trop/Trop | Any | MM 144 |
| Golden Ammonite | Water, Ocean | Any | Forgotten Realms | FR2MC |
| Hai Nu | Water, Ocean | Sub-Trop/Trop | Kara-Tur | KTMC |
| Hai Nu, Matron | Water, Ocean | Sub-Trop/Trop | Kara-Tur | KTMC |
| Imp, Blood Sea (Vapor) | Water, Ocean | Sub-Trop/Trop | Dragonlance | DLMC |
| Jellyfish, Giant | Water, Ocean | Tropical | Any | MAII 74 |
| Jellyfish, Giant (Sea Swarm) | Water, Ocean | Tropical | Any | MAII 74 |
| Kalothagh (Prickleback) | Water, Ocean | Any | Dragonlance | DLMC |
| Krakentua, Female | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Krakentua, Male | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Lycanthrope, Wereray | Water, Ocean | Tropical | Ravenloft | RVIII 83 |
| Lycanthrope, Wereshark | Water, Ocean | Any | Any | MAII 82 |
| Merman | Water, Ocean | Temperate | Any | MM 249 |
| Merman, Leaders | Water, Ocean | Temperate | Any | MM 249 |
| Nautilus, Giant | Water, Ocean | Any | Any | MAI |
| Ningyo | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Ningyo, Chieftain | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Ningyo, Leader | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Otter, Sea | Water, Ocean | Any | Any | MM 244 |
| Reaver | Water, Ocean | Any | Ravenloft | RV 45 |
| Sea Spawn, Master | Water, Ocean | Any | Ravenloft | RVIII 96 |
| Spirit Folk, Sea | Water, Ocean | Temp/Trop | Kara-Tur | KTMC |
| Strangleweed | Water, Ocean | Sub-Trop/Trop | Any | MM 293 |
| Tako, Female | Water, Ocean | Temp/Trop | Any | MM 336 |
| Tako, Male | Water, Ocean | Temp/Trop | Any | MM 336 |
| Tako, Young | Water, Ocean | Temp/Trop | Any | MM 336 |
| Tortle, Snapper | Water, Ocean | Any | Savage Coast | RSCE 126 |
| Triton | Water, Ocean | Any | Any | MM 347 |
| Triton, Exceptional | Water, Ocean | Any | Any | MM 347 |
| Triton, Leader | Water, Ocean | Any | Any | MM 347 |
| Triton, Mage | Water, Ocean | Any | Any | MM 347 |
| Triton, Priest | Water, Ocean | Any | Any | MM 347 |
| Turtle, Giant, Sea | Water, Ocean | Any | Any | MAII 108 |
| Urchin, Black | Water, Ocean | Any | Any | MM 354 |
| Urchin, Green | Water, Ocean | Any | Any | MM 354 |
| Urchin, Red | Water, Ocean | Any | Any | MM 354 |
| Urchin, Silver | Water, Ocean | Any | Any | MM 354 |
| Urchin, Yellow | Water, Ocean | Any | Any | MM 354 |
| Vurgen (Gulper Eel) | Water, Ocean | Any | Forgotten Realms | FR1MC |
| Whale, Common | Water, Ocean | Any | Any | MM 358 |
| Whale, Giant | Water, Ocean | Any | Any | MM 358 |
| Whale, Killer | Water, Ocean | Arctic | Any | MM 358 |
| Whale, Leviathan | Water, Ocean | Any | Any | MM 358 |
| Whale, Narwhal | Water, Ocean | Arctic/Sub-Arctic | Any | MM 358 |
| Zaratan | Water, Ocean | Tropical | Al-Qadim | MM 372 |