The best aquatic monsters in DnD

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

Setting up a meeting for an aquatic environment can take 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 different encounter ideas for your game.

Updated February 7, 2026 by Jerel Levy: With more companion content available and even more water setting options, we've updated this list to include a few more water creatures that you can use for a few different occasions in Dungeons & Dragons. Whether you're planning an entire underwater campaign, need a way to get them underwater, plan to ambush them on a boat trip, or want a fast water monster for an impromptu battle, we have monsters of all types to fit into any situation.

24

Seth The Shapeshifting Dragon

Don't let its origins fool you

This mighty dragon is separate from the others on this list because it comes from the release of Misplaced Monsters: Volume One. Working with Extra Life for Children's Miracle Network Hospitals to raise funds, several kids got to design their own monsters that eventually turned into full-fledged options for any campaign.

Seth the Shapeshifting Dragon is a very powerful dragon that is completely invisible when submerged in water, has a breath weapon that shoots freezing water, and has ridiculous bursts of speed to catch any creature that tries to escape. Seth can change shape at will, has super speed that disadvantages any creature that tries to attack him while active, and his Riptide Breath fires a cone that deals heavy damage to anyone caught in it. It's a monster that will present a real challenge.

23

Lorwyn Merrow

Cunning and cunning cousins

Unlike their evil cousins, the Merrow of Lorywn, found in Lorwyn: First Light, they are described as proud and diplomatic. They are great with language and can fight anyone in a verbal duel, so they are great for a campaign where you need to establish a connection between the inhabitants of the sea and the inhabitants of the land. They are also great for showing a fun mix of how aquatic creatures are shown and treated.

Shadowmoor and Doublespeaker Merrow are cunning and will easily trick an adventuring party out of everything they own if given the chance. If you play with this variant, you will lose your treasure and life as described in Lorwyn: First Light. These are all great opportunities for aquatic campaigns that will give players the opportunity to talk and interact with intelligent but cunning creatures.

Frost Giant of evil Water

Amphibious giants you should fear

If you want to add a more distinctive water giant to your campaign and don't want to rely on a generic frost giant, the Frost Giant of Evil Water provides some key specs that will come in handy. These giants who betrayed the order are gifted with the ability to breathe underwater and are equipped with items such as harpoons to help them hook and drag creatures into the sea.

They are generally evil and can be a great disruptor in a water campaign, especially when placing one deep underwater or letting one drag a party down into the depths. They're also not as powerful as Frost Giants, so you can use them without worrying about destroying the party in one hit.

22

Merfolk

Under the sea

Not every monster has to be an enemy. If you want to have underwater civilizations, the basic Merfolk work perfectly as a “common” to your story, although their group can still be a challenge for low level characters.

They also have a CR six variant that allows them to hit harder and have access to some water-related spells like Control Water so they don't have to be just weak minions or commoners during the adventure.

21

Kuo-Toa

With strange gods

The Kuo-Toas are small fish-like amphibious humanoids who once lived in coastal areas, but human settlements have driven them deeper inland. Because of this, your party is likely to find them in isolated coastal caves or underground waters.

With their low stats and CR, these creatures aren't a real challenge in small numbers. But their cult behavior and their different variants make them a real threat even for 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

Although Bullywugs are officially related to the swamplands, humanoid frogs lend themselves easily to aquatic adventures, so you have an interesting option here with the warrior Bullywug and the sage variant for a stronger monster.

They are Fey and thus escape the conditions that affect humanoids. Sage in particular is quite strong due to their liberal use of Ray of Sickness. They can also make a weapon attack in the same turn.

19

Sahuagin

Sea robbers

Sahuagin is a perfect choice for lower levels. These underwater raiders can be quite ruthless, commanding sharks to do their bidding, so you can add them as minions for upcoming battles. They also have an advantage against people who are wounded, making them more lethal during combat.

They can also come to the surface, so they are not exclusively underwater (sharks are, however). After a few hours out of the water they will have to dive, but your players probably won't care about their health.

18

Robber

Pay attention to the song

Sailors tell legends of the harpies' irresistible songs and the many sailors who met their grim end after the song began. Harpies are iconic monsters in a lot of fiction, and they make for challenging and memorable encounters in your D&D game.

Even though they only have one CR, if your players can't resist their enticing 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 also be used against higher level characters. For an even more action-packed atmosphere, try the home sirens from the harpy stat block; just replace their flying speed with swimming speed.

17

Pirate

Raise the colors

If you don't want things to go underwater, pirates are always a likely encounter, whether they're part of the story or just one of the more likely random encounters at sea. They are also all very charming as they can often induce this condition.

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

16

Merrow

Fishermen become… Fishermen?

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

While they are mostly the 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 would be no witches at sea

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

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