In Dungeons & Dragons, you'll be used to playing in all sorts of campaigns, whether hunting monsters terrorising the local towns or stopping thieves in a city. However, a standard deviation from the typical campaign is an aquatic adventure, sailing the seas and battling pirates, sea monsters and all manners of dangers that come with the cruel sea. Although this can be a nice way to spice up your tabletop roleplaying, it can't be understated that aquatic campaigns can sometimes be difficult.
Any Dungeon Master knows that it's not as simple without there being many taverns to rest in, towns to visit, and an environment that consists of forcing the player to constantly travel throughout most of their days. As well as this, some of the more typical encounters like a merchant, a traveler in need, or standard predators like wolves can't be integrated so easily in more water-based environments. So to avoid the stress that can come with thinking up encounters, here are some to get you sorted.
6 A Battle Between Ships
When you sail the seas, there's always the chance you're going to come across another ship. However, instead of the typical encounter where a pirate ship comes to attack our adventures, why not add a little more chaos into the mix?
Two ships are locked mid-battle, where players can steer their ship closer and aid one of them, or end up finding themselves mistaken as some sort of cavalry and being attacked too. It makes a sea battle more engaging, and is a good way to introduce NPC's post-battle from the surviving ship.
Not to mention, this is a way for you to make your world feel more alive. Instead of there being a ship coming for the players alone, it's instead showing a battle the players weren't previously in and was bound to happen without their involvement. It's a nice way to imbue some atmosphere by making players realise the world is a living place and other folks are sailing the seas with them and engaging in their own adventures.
5 How A Siren Got Her Groove Back
A fun encounter is always to turn the player's expectations against them. When most Dungeons & Dragons players think of a siren, they think of a dangerous and hypnotic sea creature that will try to lure them and their crew to death. So what happens when they come across a siren's song, but it sounds bad? Not terrible, but some notes are flat, the breath control is awful. You can even have players roll a Wisdom save to resist the siren's melody but have the DC just be very low.
The players come across a siren on a rock who isn't even trying to lure in sailors. When confronted will reveal she's practicing her singing. Unlike her sisters, her song doesn't beguile any passing sailors, so they cut a deal with the party: they could help the siren get better at singing, and in return they won't use their song to mesmerise any sailors to their doom. This could be a fun challenge, especially if there are any Bards in the party who can show a siren how to do a proper vibrato.
4 The Mariner's Revenge
Based on the song of the same name, this is an encounter for the types of players who love to roleplay and converse with NPCs. When players land upon the shore of an island or are coming back to their ship, they will come across the body of a young adult man. Though they might think he's dead, upon closer inspection the players will realise the man is alive and washed up on shore. This encounter will be every DM's treat.
This is an NPC who went out sailing to track down a man who had ruined his mother's life. Just as he found the ship, a storm erupted, and a whale devoured the ships, leaving him and the man the only survivors, trapped in the whale. However, what happened when he confronted the man, and how he ended up washed ashore, is up to you. Did he spare his enemy, or is he a murderer? This is a good starting point for a memorable NPC encounter.
3 It's Like That Movie
The only thing possibly worse than coming across a pirate ship in the sea, is to find a sinking ship across the sea. So, when the party stumbles across luxury ship way out in the ocean, what are they going to do? This is one of those encounters which can be a great skill challenge or a moral one, maybe forcing the party to pick and choose who they save because they might not have enough space on their ship.
At the same time, if you're looking for a way to introduce a host of different NPCs, especially ones that aren't typically going around the sea often, then this is the encounter for you. Just hope that your party actually tries to save the survivors instead of perhaps looting the ship and sailing away.
2 The Unsurfaced Island
If you're out of both encounters and even side quests, then this situation is perfect for you. As the players set sail, the ocean shakes, and they witness an island break the surface of the sea and rise out of the waters. Where did the island come from? What's on it? Is it safe or some tempting adventure? That's for you to decide, but it's safe to say having this island have a small dungeon on it can't hurt.
This is a way for players to get a unique kind of encounter while also leading into a potential side quest that could be a nice break pacing-wise for the campaign or even be a nice way for characters to test out new gear or abilities, especially if they've recently leveled up. But there's always the chance to make the dungeon a lot deeper than they anticipated and a lot more dangerous, leading to sessions worth of spelunking in this tomb, finding out its story and perhaps even ending up in someplace like the Underdark.
1 A Sailing Drink
One of the most difficult things about an aquatic Dungeons & Dragons campaign is the lack of common resources that are in a normal campaign. Such things like villages, town guards, and taverns are now much more of a rarity. That's where A Sailing Drink comes in, a ship that is exclusively a tavern of the seas, sailing during the day and stopping at sunset. There could even be an added magical element in which when the ship stops that a port forms allowing other ships to dock for the night.
It's a nice way to have a pit stop for a campaign where players are mostly always on the go, and with it being a tavern that sails around, it isn't too ridiculous for it to appear often. This is a convenient method to putting a tavern into your aquatic-themed campaign without having to railroad your players into stopping at every port town they pass by.