Summary

  • Aquatic adventures in Dungeons & Dragons can be some of the most memorable experiences for players, with modules set in uncharted waters offering unique opportunities for exploration.
  • When setting up encounters for aquatic settings, it's important to be prepared and do research. Knowing about common and interesting inhabitants, such as Kuo-Toas and Merrows, can help create engaging encounters for your game.
  • From lowly fishmen to ancient aberrations, the deep waters hold horrifying enemies in Dungeons & Dragons. The most powerful and feared of all is the Kraken, a gargantuan monstrosity that can pose a challenging and deadly threat to even the highest-level parties.

Aquatic adventures, whether they be on a ship, underwater, or even in the elemental plane of water, can be one of the most memorable adventures in Dungeons & Dragons. Many modules are set around exploring uncharted waters, and they are one of the favorite biomes for players to experience.

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Setting up encounters for aquatic settings might require a lot of preparation and research. But knowing some of the most common and interesting inhabitants of these biomes can help you come up with various encounter ideas for your game.

Updated on February 11, 2025, by Lucas Olah: If you're looking for more creatures for an aquatic setting, whether they are sailors, water-based creatures, or monsters that linger beneath the surface, D&D has you covered. In fact, these monsters were updated by the 2024 Monster Manual, which means they're even stronger, so you can throw them in your players' path. Time to see what changed with the monsters that were already here and add a few extra choices so you have more options.

22 Merfolk

Under The Sea

Art by Andrea Piparo

Monster

Challenge Rating

Merfolk Skirmisher

1/8

Merfolk Wavebender

6

Not every monster needs to be an enemy. If you want to have underwater civilizations, the basic Merfolk works perfectly to be the 'commoner' of your story, though a group of them can still be a challenge for low-level characters.

They also have a CR six variant, which allows them to hit harder and have access to some spells that relate to water, such as Control Water, so they don't need to be just weak minions or commoners during the adventure.

21 Kuo-Toa

With Weird Gods

Art by Eric Belisle

Monster

Challenge Rating

Kuo-Toa

1/4

Kuo-Toa Whip

1

Kuo-Toa Monitor

3

Kuo-Toa Archpriest

6

Kuo-Toas are small fish-like amphibious humanoids that used to live in coastal areas, but human settlements drove them deeper into the ground. Because of this, your party is likely to find them in isolated coastal caves or underground bodies of water.

With their low stats and CR, these creatures are not a real challenge in small numbers. But their cult-like behavior and their different variants make them a real threat even to mid-level parties at higher numbers, especially now that we have more options between the low-CR Kuo-Toa and the high-CR Archpriest.

20 Bullywug

From The Swamp To The Sea

Art by Sean Murray

Monster

Challenge Rating

Bullywug Warrior

1/4

Bullywug Bog Sage

4

Though Bullywugs are officially related to swamp areas, humanoid frogs easily fit aquatic adventures, so you have an interesting option here with the Bullywug Warrior and the sage variant for a stronger monster.

They're Fey and thus escape from conditions that affect humanoids. The sage, in particular, is relatively strong thanks to their free use of Ray of Sickness. They can also make a weapon attack on the same turn.

19 Sahuagin

Sea Raiders

Art by David Auden Nash

Monster

Challenge Rating

Sahuagin Warrior

1/2

Sahuagin Priest

2

Sahuagin Baron

5

A perfect option for lower levels is the Sahuagin. These underwater raiders can be quite ruthless and command sharks to do their bidding, so you can add them as minions for the battles to come. They also have an advantage against people who are hurt, so they get deadlier as the fight goes on.

They can go to the surface, too, so they're not exclusively underwater (the sharks are, though). They will need to submerge after a few hours out of the water, but your players will probably not worry about their well-being.

18 Harpy

Beware The Song

Art by Mark Zug

Monster

Challenge Rating

Harpy

1

Sailors tell legends about the irresistible songs of the harpies and the many seafarers who have succumbed to a grim end once the singing starts. Harpies are iconic monsters in many works of fiction, and they make for challenging and memorable encounters in your D&D game.

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Although they only have a CR of one, if your players fail to resist their luring song, an encounter with harpies can become extremely dangerous. Harpies are great monsters for low to mid-level parties, but with some adjustments, they can even be used against higher-level characters. For an even more aquatic flair, try homebrewing sirens from the harpy stat block; just replace their flying speed with swimming speed.

17 Pirate

Hoist The Colours

Art by Alexandre Honoré

Monster

Challenge Rating

Pirate

1

Pirate Captain

6

Pirate Admiral

12

Unless you want things to go underwater, pirates are always a likely encounter to appear, whether they're part of the story or just one of the most likely random encounters to happen at sea. They're all very charming, too, as they can trigger this condition often.

If your party is already strong enough to deal with the basic pirates, the high-CR variants can cause significant damage, especially now that pistols are more common among NPCs with the 2024 version of the manual.

16 Merrow

The Fishermen Become The... Fished?

Art by David Auden Nash

Monster

Challenge Rating

Merrow

2

Merrows are the classic fish people in D&D, even before 5e. These large monstrosities hunt lost sailors, attack and capture ships with their fast swimming speed and their large harpoons, and are a constant threat in any aquatic campaign.

Even though they are mostly an enemy in the early game, they can still be used very effectively at high levels as minions for stronger monsters. They can separate weaker party members with their harpoon attacks and make player characters more vulnerable to more dangerous enemies.

15 Sea Hag

And They Thought There Wouldn't Be Witches At Sea

Art by Lorenzo Mastroianni

Monster

Challenge Rating

Sea Hag

2

Hags are one of the most popular monsters to fight against in D&D, so why would you not use them just because the adventure is at sea? After all, they have an aquatic variant in the form of the Sea Hag.

It's not the strongest Hag out there, but with a CR of two, you can be quite the nuisance during the adventure's beginning and maybe even use her for the party's first boss fight if they haven't had one already.

14 Deep Scion

The Price To Survive

Ghosts of Saltmarsh by Grzegorz Rutkowski

Monster

Challenge Rating

Deep Scion

3

Terrifying though they may be, deep scions were once regular humanoids that carried out normal lives. They come about through an ancient and well-guarded ritual known to powerful deep-dwelling beings who offer a life of servitude to souls lost to the sea in exchange for preventing them from drowning.

Unfortunately for those who take this deal, the life of servitude they're offered is nothing like the life they claimed before.

Over the course of the ritual, those who become deep scions completely lose themselves to the worship of their underwater masters. So much so that they physically transform into slimy creatures with tentacles for hair and consider this new form their true body, as opposed to the shape of their old life that they maintain the ability to take on.

Deep scions act as the eyes and ears of the ancient abominations they serve by resuming their old lives as if nothing had ever happened. However, when called upon to act by their new masters, these creatures take pleasure in carrying out their orders, even if it comes at the cost of the ones they held dearest in their previous lives.

13 Water Weird

Face Water Itself

Art by Crystal Sully

Monster

Challenge Rating

Water Weird

3

Water weirds are a fun challenge, especially if you want to take your players by surprise. They're basically a sentient water spout, and can fight as long as they're connected to their source, which means that disconnecting them is a good strategy for the players.

This fight is extra fun if you manage to have it underwater, as the Water Weird just blends with the surrounding water, becoming invisible in the process. Not to mention that fighting underwater is harder in itself.