d100 Encounter
16 – 20 2d4 swarms of quippers
21 – 25 A sunken galleon with a 50% chance of a random treasure hoard inside (roll on the Treasure Hoard: Challenge 5–10 table in chapter 7 of the Dungeon Master’s Guide)
26 – 30 1d4 plesiosauruses
31 – 35 3d6 reef sharks
36 – 40 An abandoned bathysphere
41 – 50 1d4 giant constrictor snakes
51 – 55 2d4 hunter sharks
56 – 60 1d3 sahuagin priestesses with 2d10 sahuagin
61 – 65 An empty castle made from coral
66 – 70 1d4 killer whales
71 – 75 1d10 merrow
76 – 80 An eerie statue of a squatting humanoid, with bat wings on its back and tentaclsprouting from its face es
81 – 85 1d4 water elementals
86 – 90 1 sahuagin baron with 2d8 sahuagin
91 – 96 1d4 giant sharks
97 – 99 1 marid
00 1 storm giant
Underwater Encounters (Levels 11–20)
d100 Encounter
01 – 10 1 sahuagin baron with 1d4 sahuagin priestesses and 2d10 sahuagin
11 – 35 1d10 killer whales
36 – 40 A ghost ship passing overhead, containing 2d6 + 10 ghosts
41 – 60 1d6 giant sharks
61 – 65 A 1-mile-radius sphere of effervescent water that allows air-breathing creatures to breathe water while in the sphere
66 – 75 1d10 water elementals
76 – 80 A shimmering, blue-green portal to the Elemental Plane of Water
81 – 90 1d4 marids
91 – 96 1d3 storm giants
97 – 99 1 dragon turtle
00 1 kraken