The Best Monsters For An Aquatic Setting In DnD

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.

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

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

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

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

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

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 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

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?

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

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

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

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.

12

Water Elemental

Face Water Itself, Round Two

If you liked the previous idea but need something that hits harder, the Water Elemental is a great option. They don’t have the same water blending mechanic the Weirds do, but it makes sense to say that they blend in underwater.

Regardless, they are strong, can pass through people with ease, can knock them prone, and even suffocate them as they engulf the target and cause further damage to them. Its mechanics are pretty fun.

11

Skum

A Powerful Minion

Some monsters are so powerful that even their minions can be a challenge for most players, like the Aboleth’s minion, the Skum. It 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 a disadvantage on their wisdom saving throws, making them more susceptible to the Aboleth’s charm.

10

Kraken Priest

Guess Someone Has To Worship That

If your party is not ready to face the mighty Kraken, its 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 Merrows 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.

9

Aboleth

Obey Me, Weakling

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 in an aquatic campaign.

8

Morkoth

Mini Kraken

The Morkoth is similar in appearance to a Kraken, but with the notable difference in 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.

7

Marid

Water Genies

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.

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.

6

Wastrilith

Water Demon

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.

5

Storm Giant

I Am The Storm That Is Approaching

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.

4

Dragon Turtle

For Tougher Parties

Fighting a dragon in its lair is one of the most exhilarating experiences you can have when playing D&D. Still, 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.

3

Leviathan

For Even Tougher Parties

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 near 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.