Dungeons & Dragons is filled with countless monsters that a Dungeon Master can include in a given campaign. More monsters are added in almost every new D&D setting, giving DMs even more options to throw at their players. The monsters included in a campaign help set the tone and can also work to establish a specific location with the world. Some monsters can be found just about anywhere, but others are extremely specialized for certain environments.

Aquatic monsters are among the most specialized, as they feature unique movement modes and completely alien physiologies. Most player characters will be out of their element when fighting underwater. Using the wide variety of sea monsters 5e D&D has to offer is a great way to keep them on their toes.

Updated on December 24th, 2023 by Louis Kemner: Aquatic monsters are an underserved category in D&D 5e's monster books, making a naval campaign hard to populate. Nonetheless, there are some standout options. This list of aquatic D&D monsters has been updated to adhere to CBR's current publication standards.

20 Skum Are Psychic, Alien-Like Monsters That Serve Aboleths

Skum are horrible creatures introduced in the Ghosts of Saltmarsh premade D&D 5e campaign. Skum are corrupted by the influence of another powerful aquatic creature, often an aboleth. Despite their straightforward brutality, skum have several more alien abilities that set them apart from standard melee monsters.

A skum's psychic corruption has left them immune to the frightened and charmed conditions, covering a common weakness for brute enemies with low Wisdom and Intelligence scores. Additionally, they have a vicious Mind-Breaking Touch power that inflicts massive psychic damage and imposes disadvantage on Wisdom saving throws. This is perfect for combining with other, more powerful psychic water monsters in D&D 5e.

19 Water Elementals Are Aquatic Warriors That Can Be Summoned

Fewer creatures are more natural aquatic monsters in D&D 5e than water elementals. They are the magical essence of water animated into a physical and threatening form. Water elementals can squeeze through almost any space, whether underwater or on dry land. Their unique Whelm attack can grapple multiple creatures and deal damage each turn.

Water elementals aren't the most dangerous sea monsters in D&D 5e. Nonetheless, they're very ubiquitous. Almost any villainous spellcaster could summon a water elemental to add some muscle. Furthermore, they're less reasonable than the most sentient water creatures filling most oceans in D&D 5e.

18 Kraken Priests Serve Krakens With Their Spellcasting and Electric Attacks

Kraken priests are dangerous spellcasters who have devoted themselves to the service of a kraken in hopes of currying favor and siphoning some amount of power off in the process. Kraken priests gain a swim speed and resistance to nonmagical bludgeoning, piercing, and slashing damage, making them challenging water enemies in D&D 5e to land hits on.

A kraken priest's connection to their master grants them some innate spellcasting, including Evard's Black Tentacles, Control Water, Water Walk, and even the ability to cast Command at will. Introducing a kraken priest into a D&D campaign is a great way to foreshadow an even more powerful looming threat.

17 The Maw Of Sekolah is a Decorated Monster Representing the Sahaugin God

The Maw of Sekolah is another lethal D&D 5e sea creature from the Ghosts of Saltmarsh book. It is an enormous, two-headed shark summoned by sahuagin cultists in rituals to their dark shark god. The Maw of Sekolah boasts two Legendary Resistances each day and a handful of legendary actions despite its relatively low Challenge Rating of 7.

With these, the Maw can move up to its 50-foot speed after another character's turn, attempt to smell out its prey with a Perception check, or even attack every creature within 60 feet of it with gnashing shark mouths. This massive shark is the perfect D&D sea monster to savage any unfortunate adventurers who fall unexpectedly overboard.

16 Water Elemental Myrmidon Are Like Elemental Knights

Water elemental myrmidons are stronger versions of water elementals magically bound into plate armor. This gives them significantly higher defenses, coupled with some unique offensive options over their more conventional kin. Most notably, they wield tridents in combat rather than using their natural form.

A water elemental myrmidon's high Armor Class and hit points make them a suitable aquatic monster in D&D 5e to show that a greater villain means business or as a rogue threat in their own right. Their Freezing Strikes attack is particularly damaging to player characters already slowed by fighting underwater.

15 Aboleths Are Eldritch Monsters That Haunt Dark Waters

Aboleths are eldritch and iconic D&D 5e monsters, inspired by the terrors of the deep found in the work of H. P. Lovecraft. Aboleths reside in the depths of ancient seas and lakes. A fixture of D&D since the game's first edition, aboleths are ancient beings that use their psychic abilities to enslave other creatures.

Aboleths harbor an ancient resentment against D&D's gods, making them the perfect foes for a party with a devout cleric or paladin among its ranks. Their ability to enslave other creatures means that an aboleth might be found fighting alongside many other, disparate creatures. This can help ensure that fighting an aboleth's thralls is always a surprise.

14 Marids Are Unpredictable, Watery Genies

D&D genies come in numerous forms corresponding to air, earth, fire, and water. Marids, tied to the Elemental Plane of Water, are traditionally chaotic neutral beings that may or may not be antagonistic towards the player characters. They can play any role in an aquatic D&D campaign, from strange patron to opportunistic menace.

However, marids are particularly dangerous D&D sea enemies if angered. They can cast potent spells like Conjure Elemental, Invisibility, Plane Shift, and sometimes even Wish. Their tridents alone can be used to devastating effect in melee, making these creatures equally powerful potential friends or foes.

13 Morkoths Are Sinister, Hypnotic Squids

Appearing first in Volo's Guide to Monsters, morkoths are massive, squid-like creatures found within flooded lairs on secluded islands. Similarly to an aboleth and other D&D sea monsters, a morkoth can manipulate the minds of adventurers and wield hypnosis as one of its primary weapons.

Morkoths are habitual hoarders, and they fill their lairs with powerful magic that allows them to track down items, cause creatures to lose track of their possessions, and even make water breathable and clean as air. Venturing to a morkoth's lair is the perfect hook for a D&D party voyaging on the high seas.

12 Wastriliths Prove That Not Even the Ocean is Safe From Demons

A wastrilith is a potent amphibious demon in D&D 5e, introduced in Mordenkainen's Tome of Foes. Wastriliths are known to corrupt water with their very presence. When a wastrilith comes into contact with water, the effect turns it incredibly toxic and murky almost immediately.

A wastrilith is an even more deadly sea enemy in D&D 5e when accompanied by other demons. Their corrupted water is poisonous to players, but heals demons when consumed. A wastrilith can make an entertaining change of pace from the more eldritch and abomination-themed aquatic enemies in D&D 5e.

11 Juvenile Krakens May Be Young, But Can Still Terrorize Ships

The kraken is one of the most iconic aquatic enemies in D&D 5e. However, it's also an endgame enemy meant for very powerful parties. Lower-level adventurers will struggle a suitable amount against the younger and weaker juvenile kraken introduced in the Ghosts of Saltmarsh premade D&D module.

A juvenile kraken has less extreme versions of a kraken's most devastating abilities in D&D 5e. Its attacks automatically grapple creatures to fling them further away to blight melee enemies, while ink clouds and lightning strikes make life unpleasant for ranged attackers and magic users. Despite its youth, a juvenile kraken is one of the most dangerous D&D 5e sea monsters for mid-level parties.

10 Storm Giant Quintessents Are Masters of Water, Lightning, and Wind

While D&D 5e's amphibious storm giants are already powerful in their own right, the storm giant quintessent is a much more dangerous being with a challenge rating of 16. Completely in sync with the elements and nature, a storm giant quintessent can become one with natural disasters themselves, such as a harsh blizzard or storm.

When it comes to combat, a storm giant quintessent can attack with its Lightning Sword twice each turn, dealing an astonishing 9d6+9 lightning damage on each hit. Additionally, this creature can use its legendary actions to displace other creatures with a gust or attack from afar with lightning bolts.

9 Dragon Turtles Wreck Ships and Breathe Deadly Steam

Dragon turtles are a constant aquatic monster threat in D&D 5e that adventurers should always be wary of while traveling on the high seas. While not as dangerous as ancient dragons, these D&D sea monsters boast a staggering 341 hit points and have an Armor Class of 20. They're one of the sturdiest monsters parties might run into.

A dragon turtle can expel a deadly blast of steam that deals a whopping 15d6 damage to anything unfortunate enough to get in its way. Alternatively, it can make three high-damage attacks that can devastate players and ships alike. Defending a coastal town from a dragon turtle attack could be an entire adventure in and of itself.

8 Olhydra Is Deadly In Her Watery Lair

Also known as the Crushing Wave, the Dark Tide, or the Well of Endless Anguish, Olhydra is the Elemental Princess of Evil Water, one of D&D's four evil elemental princes. Though she is most likely to be encountered via her cultists — who include pirates, sailors, and all manner of lost souls — she is a force to be reckoned with on her own.

Olhydra can cast Wall of Ice at will and can conjure water elementals to aid her in her fight. Anywhere she makes her lair becomes infused with her power, allowing her to suck creatures down into murky tide pools or lock the area in a dense, freezing fog. Her inherent connection to water makes her one of the most dangerous aquatic monsters in D&D 5e.

7 Leviathans Are Iconic Sea Beasts That Command the Tides

The leviathan is one of the most dangerous opponents in D&D that can be encountered beneath the waves. With a challenge rating of 20 and access to powerful Legendary Resistances, the leviathan is a D&D 5e sea monster that can be the final boss of an entire campaign.

The scariest tool at a leviathan's disposal is its ability to create tidal waves. These waves are up to 250 feet long, up to 250 feet high, and up to 50 feet thick. They damage anyone in their area, even on a successful saving throw. These tidal waves continue to move throughout the fight, potentially devastating an entire party in combat.

6 Elder Tempests Are Living Storms With Some Watery Attributes

An elder tempest is one of the most dangerous elemental threats players can encounter in a D&D campaign. Its status as the elemental embodiment of the storm makes it equally as comfortable over the water as anywhere else. The elder tempest is less of an aquatic D&D 5e monster and more of a sapient natural disaster.

With terrifying legendary actions like Lightning Strike and Screaming Gale, an elder tempest can attack up to four times every round. The very presence of this being dissipates all flame and fog and causes all ranged attack rolls to be made at disadvantage. The party must fight an elder tempest on its own terms in D&D 5e.

5 Krakens Destroy Ships and Port Towns With Incredible Ease

Few D&D aquatic monsters are as iconic in fantasy as krakens. Like the elder tempest, krakens possess a startlingly high challenge rating of 23. Dealing damage to a kraken can be an endeavor in itself. They are immune to several damage types on top of the inherent challenges of fighting underwater in D&D 5e.

A D&D kraken's offensive capabilities are just as impressive, since they attack up to three times a turn for massive damage. They can provide a constant threat of elemental damage, physical attacks, swallowing party members, and even blinding the party by releasing ink clouds as a legendary action.

4 Ancient Gold Dragons Like Water and Have Various Breath Attacks

Ancient gold dragons are not just one of the deadliest aquatic monsters in D&D, but also one of the most powerful creatures in the game. Besides being able to shapeshift, the Ancient gold dragon has an AC of 22 and a catastrophic breath attack that deals an overwhelming 13d10 fire damage.

Luckily for players, gold dragons are traditionally reclusive, good-aligned beings who are more inclined to help players rather than attack them. While a gold dragon, with its powerful fire breath, might not seem like a sea monster, D&D 5e makes these creatures powerful swimmers equally at home on land or beneath the waves.

3 Ancient Dragon Turtles Are Apocalyptic Threats on the High Seas

Dragon turtles are already some of the most dangerous sea monsters D&D 5e has to offer. However, Fizban's Treasury of Dragons introduces an older and even more threatening version. An ancient dragon turtle has lived long enough and amassed enough power to become a Mythic Monster.

Ancient dragon turtles are even harder to kill than their mundane kin. The high defenses and vicious Steam Breath are still there. On top of that, it can regain all of its hit points the first time it's reduced to 0. When it does, it gains powerful new Mythic Actions like a storm aura around it, signaling that the fight has truly begun.

2 Demogorgon Is Comfortable Fighting in Water if Need Be

One of the most iconic creatures in D&D is also one of the most devastating D&D 5e sea monsters DMs can threaten their players with. Demogorgon, the Prince of Demons, the Master of the Spiraling Depths, resembles a massive, two-headed ape with tentacled limbs.

Though he doesn't have the aquatic trait, Demogorgon does have a 50-foot swim speed and is quite at home deep in the waters of his demonic lair. Demogorgon's immense D&D 5e statblock, legendary actions, demonic powers, and more make him more of a challenge than many parties can manage, even if they're used to fighting underwater.

1 Tromokratis Is the Lord of the Sea on Theros

Tromokratis is an almost unstoppable kraken used to demonstrate Mythic Odysseys of Theros' Mythic Monsters system. It lacks some of the D&D 5e kraken's abilities, such as lightning and ink clouds. In exchange, however, it gets even more immense physicality. Its attacks never miss and deal immense damage, on top of its high defenses.

Its Mythic status makes Tromokratis such a dangerous sea monster in D&D 5e. The first time players fight through its immense hit point pool, Tromokratis doesn't die. Instead, its carapace cracks to reveal four hearts. Players have to climb or swim around Tromokratis to target these hearts. If even one remains, it won't die.