Highlights

  • 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 August 10, 2023 by Chris Stomberg: The human fear of what lurks in the deepest of depths is a dread that has existed since the beginning of time. Though we may have eventually learned how to swim and survive inside of and nearby large bodies of water, it's impossible to know for certain what lies in the deep, cold dark of rivers, lakes, and oceans. This fear has spurred on the creation of some of Dungeons & Dragons' most horrifying enemies, from lowly and barely sentient fishmen to ancient, all-powerful aberrations as old as time itself.

15 Kuo-Toa

Drawing of the fish-like humanoids, Kuo-Toa
Kuo-Toa via Wizards of the Coast

Challenge Rating

1/4

Size and Creature Type

Medium Humanoid

Notable Traits

Advantage on escaping from grapples Able to see invisible and ethereal creatures Sensitive to sunlight

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.

14 Harpy

Half human, half bird harpy sitting on a rock
Harpy via D&D Beyond

Challenge Rating

1

Size and Creature Type

Medium Monstrosity

Notable Traits

Can charm multiple creatures with its Luring Song

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.

Although they only have a challenge rating 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 for swimming speed.

13 Merrow

Fish monster with a harpoon
Merrow via D&D Beyond

Challenge Rating

2

Size and Creature Type

Large Monstrosity

Notable Traits

Able to pull creatures towards it with harpoon attacks

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 for 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.

12 Deep Scion

Ghosts of Saltmarsh by Grzegorz Rutkowski
Ghosts of Saltmarsh by Grzegorz Rutkowski

Challenge Rating

3

Size and Creature Type

Medium Monstrosity

Notable Traits

Change Shape Psychic Screech: stun nearby enemies and transmit memories to master

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.

11 Wereshark

A shark swimming in blue water
A fleshtearer shark (4E Monster Manual 2 Art Gallery) by Jim Nelson 

Challenge Rating

4

Size and Creature Type

Medium Humanoid

Notable Traits

Can change shape to humanoid, hybrid, and shark forms Advantage on attacking damaged foes

Lycanthropes are fascinating monsters to include in your D&D game, and if your game is set in an aquatic setting, then weresharks can be a great inclusion in your encounters. They can be menacing pirates, memorable NPCs, or terrifying hunters who roam the seas.

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These lycanthropes can have a rich backstory and connection to important deities (so they can be an integral part of the game's story), as well as a challenging opponent for your players to face. With a challenge rating of four and unique abilities such as Blood Frenzy, they can be a challenging boss for low to mid-level parties.

10 Skum

Slimy grey creature with long arms and multiple tantacles
Skum (Ghost of Saltmarsh) by Shawn Wood

Challenge Rating

5

Size and Creature Type

Medium Aberration

Notable Traits

Immunity to charm and fear Deal large amounts of psychic damage

Some monsters are so powerful that even their minions can be a challenge for most players. We will talk about the intimidating aboleth later, but their minions, skum, can be a challenging and terrifying encounter before your party has to come face to face with their master.

Even alone, a skum can be deadly with its Mind-Breaking Touch. But if paired with the aboleth, their abilities can give players disadvantage on their wisdom saving throws, making them more susceptible to the aboleth's charm.

9 Kraken Priest

A pale priest surrounded by waves of water and black tentacles
Kraken Priest (Volo's Guide to Monsters) by Chris Seaman

Challenge Rating

5

Size and Creature Type

Medium Monstrosity

Notable Traits

Innate Spellcasting Can channel the voice of the Kraken to frighten opponents

If your party is not ready to face the mighty Kraken, a Kraken priest is a perfect choice to give them a decent challenge, and a taste of what is to come. Unique to 5e, these worshipers of the legendary monster can be used alone or with a whole group of cultists and other sea monsters. They could command merrow to attack your players' ship if they get too close to the Kraken's lair.

They have powerful melee and ranged attacks that deal thunder and lightning damage, and have access to powerful spells such as control water or Evard's black tentacles to control the battlefield to their advantage.

8 Aboleth

aquatic monster with tentacles
Aboleth via D&D Beyond

Challenge Rating

10

Size and Creature Type

Large Aberration

Notable Traits

Telepathic communication Ability to enslave creatures with a strong charm effect Can afflict multiple diseases that hinder the target's survivability outside of water

Aboleths are terrifying aberrations that live deep underwater. Their lair will affect a large area of the waters they live in, and discovering and killing an aboleth can be a complete adventure on its own.

With a strong charm effect, they can force other creatures to become their minions, as we saw with the skum. With the help of their minions, and their legendary and lair actions, aboleths can be great opponents for mid to high-level parties. Because of their high intelligence and telepathic abilities, they can even be the big bad evil guy of an aquatic campaign.

7 Morkoth

morkoth kraken tentacle creature with treasure hoard in sea
Morkoth via Wizards of the Coast

Challenge Rating

11

Size and Creature Type

Large Aberration

Notable Traits

Tentacles Hypnosis Innate Spellcasting Spell Reflection

The morkoth is similar in appearance to a kraken with the notable difference that its body contains the vast treasures that it hoards. Morkoths are also directly tied to the mobile islands that they rule. Most often, the morkoth has no ability to control where the island it reigns over moves. Furthermore, morkoths were originally formed from the flesh of a dead god in the Astral Plane so their islands can be encountered in the sea, sky, or even space.

Unlike the aboleth, morkoths don't have legendary resistances nor do they have legendary actions. Even so, they are arguably more deadly opponents owing to their hypnosis ability that charms opponents, access to spells like dimension door, dispel magic, and lightning bolt, and spell reflection that can cause spells cast on the morkoth to be redirected at others nearby. Morkoths also have lair actions and are almost certain to be encountered in their lairs at all times seeing as they are one with the islands they tyrannically oversee.

6 Marid

Water Genie in white and blue robes
Marid via Wizards of the Coast

Challenge Rating

13

Size and Creature Type

Large Elemental

Notable Traits

Deals cold damage to everyone in an aura Innate Spellcasting

Genies are an integral part of any campaign that revolves around elemental planes, and if you are planning a campaign revolving around water, marids will be a natural fit. Water Genies can be unique and memorable characters for your players to face.

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As marids are not inherently evil, they can also be fun NPCs or allies to include in your game, but they are very capable of defending themselves if it comes down to it. With their high challenge rating, dangerous abilities, and powerful spell casting, they are a challenging foe to overcome even for high-level parties.

5 Wastrilith

The aquatic demon, Wastrilith
Wastrilith via Wizards of the Coast

Challenge Rating

13

Size and Creature Type

Large Fiend

Notable Traits

Magic Resistance Immunity to Poison Can pull creatures towards itself

Wastriliths are demons who rule in the waters of the abyss or the depths that have been infected by the influence of the demonic realm. Whether you want to take your party on a deadly journey into the abyss or have them face the demonic wrath in their sea travels, the wastrilith is your guy.

With a challenge rating of 13 and some extraordinary features, wastriliths can be challenging bosses for high-level parties. They corrupt the surrounding waters, damaging every creature who swims in them and even healing other demons in the vicinity.

4 Storm Giant

A Storm Giant holding a huge sword
Storm Giant via Wizards of the Coast

Challenge Rating

13

Size and Creature Type

Huge Giant

Notable Traits

Innate Spellcasting Lightning Strike

The adventurer's ship is stuck in a horrific storm. Through magic and fast decision-making, they manage to weather the storm and pass through, only to find a gigantic creature in the center of the fog. A storm giant who is controlling the rolling thunders and crashing waters.

Storm giants are the strongest giants in D&D. When it comes to the sea, they are one of the toughest creatures your party might come upon in their aquatic travels. Storm giants are also featured in one of the most popular D&D modules, Storm King's Thunder.

3 Dragon Turtle

Dragon Turtle attacking a ship from below
Dragon Turtle via D&D Beyond

Challenge Rating

17

Size and Creature Type

Gargantuan Dragon

Notable Traits

Steam Breath

Fighting a dragon in its lair is one of the most exhilarating experiences you can have when playing D&D. But there's something that can be even more terrifying than a giant dragon in its home: a dragon turtle that can snap your ship in two within seconds.

Encountering a dragon turtle is usually just about surviving, but if your party decides to face this CR 17 monster head-on, they are in for a deadly fight. With a devastating steam breath, and powerful physical attacks, this gargantuan dragon can turn a ship to shreds and decimate unprepared adventurers.

2 Leviathan

Leviathan water elemental sea serpent beside fish in ocean
Leviathan via Wizards of the Coast

Challenge Rating

20

Size and Creature Type

Gargantuan Elemental

Notable Traits

Tidal Wave Siege Monster Partial Freeze

Leviathans are the ultimate water elementals hailing from the Elemental Plane of Water. Though made entirely of water, these creatures often take the form of a giant serpent that seeks to wreak havoc on seafaring people and coastal communities alike.

The Leviathan's attacks deal a fair amount of acid damage, and it has a ridiculous swim speed of 120 feet. They are also capable of summoning giant Tidal Waves 250 feet long, 250 feet tall, and 50 feet wide that can devastate any settlement nearby the ocean as well as its inhabitants. Add legendary actions and legendary resistances to the mix and you've got a foe that can keep up with even the highest level parties.

1 Kraken

The tentacled titan, Kraken
Kraken via Wizards of the Coast

Challenge Rating

23

Size and Creature Type

Gargantuan Monstrosity (titan)

Notable Traits

Freedom of Movement Siege Monster Can strike 3 opponents with strong lightning bolts Can create an ink cloud that heavily obscures its surroundings

The most iconic monster in aquatic settings is without a doubt the legendary titan, the Kraken. Krakens are the tarrasques of the seas. They are the most powerful creature your party can face in the water, and the worst nightmare of sailors and adventurers alike.

With a challenge rating of 23, extremely powerful legendary and lair actions, and strong regional effects, Kraken can certainly put up a fight — even killing a Kraken can be the main plot of a high-level campaign. Water elementals roam around the Kraken's lair, and every sea creature within the vicinity is charmed by the titan to defend the area.

Just getting to the Kraken's lair can take multiple sessions, and few will survive the final encounter to tell the tale. A word of caution to dungeon masters though: make sure to give your Kraken legendary resistance.

NEXT: Dungeons & Dragons: Classic Endings For Your Campaign