Toxic Mangrove

The land itself is poisoned. Yellow water stands in the hollows, the air stings the eyes, and the few plants that still grow are bitter and oddly coloured. Whatever lives here has learned to live with poison, or carries it. Salt-water forest on tropical coasts, its trees standing on stilt roots that the tide covers and uncovers. A tangle of channels, mud and fish, hard to cross and easy to hide in.

Hear it

Water: Toxic River (On Patreon, Raven tier)
Toxic: Sinister Field of Mud and Geysers (In the album RPG Ambiences Vol. 3)
In the rain: Acid Rain (In the album RPG Ambiences Vol. 5)
By day: Tropical Swamp (In the album RPG Ambiences Vol. 8)
At night: Tropical Swamp at Night (In the album RPG Ambiences Vol. 8)
By boat: Rowboat on Large Tropical River (On Patreon, Guardian tier)
On the coast: Tropical Coast (In the album RPG Ambiences Vol. 8)
Sucking mud: Thorny Swamp (In the album RPG Ambiences Vol. 7)
Tides: Rough Sea (In the album RPG Ambiences Vol. 8)
Biting insects: Jungle with Insect Swarm (On Patreon, Raven tier)

For the table

Ground: hard going, about 10 km a day on foot
Water: plentiful
Foraging: fair

Hazards

Sucking mud. Firm-looking ground opens onto deep mud or peat. Alone and laden, a traveller can be held until the water rises or the cold comes.
Tides. The sea comes back faster than a walker on the flats. A causeway or a beach crossed at low tide can close behind the party.
Fevers. Warm stagnant water breeds the fevers that emptied whole expeditions before anyone knew the mosquito carried them.
Biting insects. In the warm season, clouds of mosquitoes and flies bite day and night. Sleep and tempers wear thin.
Poisoned water. Springs and pools look clear and taste of metal. Boiling does not clean them.
Choking vapours. In still hollows the vapours pool, heavy and unseen. Birds that land there do not fly off again.
Caustic mud. Some patches of mud bubble and smoke. They eat through leather in an hour, and through skin faster.

D&D 5e

Plays as: swamp, slow pace at most
Checks: forage: Survival DC 10 · find the way: DC 15 · search: DC 20
Creatures are spotted at: 2d8 × 10 ft

Poisoned water. (House rule) A creature that drinks the land’s water, boiled or not, makes a DC 13 Constitution save or has the Poisoned condition for 24 hours. Only water carried in, or made pure by magic, is safe.
Choking vapours. A creature in the vapours must hold its breath, for 1 plus its Constitution modifier minutes (never less than 30 seconds). After that it gains 1 Exhaustion level at the end of each of its turns, and loses them all as soon as it can breathe again.
Caustic mud. (House rule) A DC 13 Wisdom (Survival) check spots a patch before anyone steps in. A creature that steps in makes a DC 12 Dexterity save or takes 2d6 Acid damage, and its boots are ruined.

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.

Pathfinder Second Edition

Plays as (Pathfinder Second Edition): swamp, greater difficult terrain, about 11 km a day at Speed 25
Checks: Subsist: Survival DC 15 · Sense Direction: Survival DC 20
Random encounters: flat check DC 14 each day

Sucking mud. Quicksand (GM Core p. 107): a hidden patch about 5 m wide (Stealth +12; Survival DC 18 to spot by disturbing it). Stepping in sinks a traveller to the waist, then one step each round (neck, then under); Athletics DC 20 climbs back a step, and allies can pull with Athletics DC 20.

This product is licensed under the ORC License located at the Library of Congress at TX 9-307-067 and available online at various locations including paizo.com/orclicense, azoralaw.com/orclicense, and others. All warranties are disclaimed as set forth therein. Attribution: this rules layer is based on the following Licensed Material: Pathfinder Player Core © 2023 Paizo Inc., Designed by Logan Bonner, Jason Bulmahn, Stephen Radney-MacFarland, and Mark Seifter. Authors: Alexander Augunas, Kate Baker, Logan Bonner, Jason Bulmahn, Carlos Cabrera, Calder CaDavid, James Case, Eleanor Ferron, Steven Hammond, Joan Hong, Vanessa Hoskins, James Jacobs, Jenny Jarzabski, Erik Keith, Dustin Knight, Lyz Liddell, Luis Loza, Patchen Mortimer, Dennis Muldoon, Stephen Radney-MacFarland, Mikhail Rekun, David N. Ross, Michael Sayre, Mark Seifter, Kendra Leigh Speedling, Mark Thompson, Clark Valentine, Andrew White, Landon Winkler, and Linda Zayas-Palmer; Pathfinder GM Core © 2023 Paizo Inc., Designed by Logan Bonner and Mark Seifter. Authors: Amirali Attar Olyaee, Logan Bonner, Creighton Broadhurst, Jason Bulmahn, James Case, Jesse Decker, Eleanor Ferron, Fabby Garza Marroquín, Jaym Gates, Matthew Goetz, James Jacobs, Brian R. James, Jenny Jarzabski, Dustin Knight, Jason LeMaitre, Lyz Liddell, Luis Loza, Ron Lundeen, Stephen Radney-MacFarland, David N. Ross, Michael Sayre, Mark Seifter, Owen K.C. Stephens, Amber Stewart, Clark Valentine, Landon Winkler, and Linda Zayas-Palmer; Pathfinder Monster Core © 2024 Paizo Inc., Authors: Alexander Augunas, Dennis Baker, Kate Baker, Joshua Birdsong, Joseph Blomquist, Logan Bonner, Jason Bulmahn, James Case, John Compton, Paris Crenshaw, Adam Daigle, Darrin Drader, Brian Duckwitz, Robert N. Emerson, Scott Fernandez, Eleanor Ferron, Leo Glass, Matthew Goodall, BJ Hensley, Thurston Hillman, Vanessa Hoskins, James Jacobs, Jenny Jarzabski, Miko Kallio, Jason Keeley, Jeff Lee, Lyz Liddell, Luis Loza, Ron Lundeen, Robert G. McCreary, Philippe-Antoine Menard, Jacob W. Michaels, Dave Nelson, Jason Nelson, Tim Nightengale, Stephen Radney-MacFarland, Mikhail Rekun, Patrick Renie, Alex Riggs, David N. Ross, Michael Sayre, Mark Seifter, Chris S. Sims, Amber Stewart, Jeffrey Swank, William Thompson, Jason Tondro, Clark Valentine, Landon Winkler, Tonya Woldridge, and Linda Zayas-Palmer. If you use our Licensed Material in your own published work, please credit us as follows: Biomes, Pathfinder Second Edition rules layer © 2026 Michael Ghelfi. Reserved Material: the names of Biomes and its catalogues, its descriptions, sounds, art and code. Pathfinder is a registered trademark of Paizo Inc.; this site is not published, endorsed, or specifically approved by Paizo Inc.

Adventure hooks

A herbalist has lived thirty years in the poisoned land in perfect health, and she sells a tonic she swears is the reason. The tonic is pond water: she is well because she has swallowed a little poison every day of her life, and now she wants to move to town to meet her grandchildren.
A lord has heard that the poison yields the finest yellow dye in the kingdom and has sent his steward to fetch a barrel of it. The steward is terrified, unfailingly polite, and under orders not to come home with less than a full barrel.
The poison spreads a mile further every year, and it has a source: for a century the alchemists of the nearest town have buried their failed brews here. Their new mistress did not know, and now that she does, she has decided it would be cheaper to make sure nobody else ever finds out.
A boy from the edge of the poisoned land has tamed one of its creatures, small, bright and deadly to touch, and his father wants it killed. It has saved the boy’s life twice already, and the water it drinks from runs clear for a day afterwards.
Pirates hide their boats in the mangrove channels, and the fishermen are paid to keep quiet. One fisherman wants out, and the only safe way is to lead someone to the hideout and make it look like bad luck.
Honey hunters go into the mangrove each spring, and every year a tiger takes one of them. This year a holy man has come to bless them, and insists on going along, barefoot.
A smuggler who uses the channels at high tide pays the crab catchers in pearls to look away. The pearls are fake, the crab catchers have just found out, and the smuggler is due back tonight.
A fisherman’s boy has found a channel that ends in a perfectly round lagoon with no trees around it. He wants someone to go with him, because his father has forbidden it without saying why.

What grows here

Red Mangrove (tree). A salt-tolerant evergreen tree, usually about 6 m, raised over the water on arching prop roots, often the most seaward of the mangroves. It grows on muddy tropical coasts and estuaries of the Americas and West Africa, and its seedlings root on the tree before dropping and floating away. Its bark was a major source of tannin. Gives: Red Mangrove Bark, Red Mangrove Wood.

Animals

Tiger (man-killer, alone, by night)

Creatures

Gray Ooze (a threat to the unwary, Challenge 1/2)
Swarm of Insects (a threat to the unwary, Challenge 1/2)
Chuul (a fight to fear, Challenge 4)
Otyugh (deadly, Challenge 5)

Also met here

Flying Snake (a threat to the unwary, Challenge 1/8)
Black Dragon (deadly, Challenge 2-21)
Giant Constrictor Snake (a fight to fear, Challenge 2)
Weretiger (a fight to fear, Challenge 4)
Giant Crocodile (deadly, Challenge 5)
Hydra (deadly, Challenge 8)

To gather

Ooze Portion, Red Mangrove Bark, Red Mangrove Wood, Tiger Bone, Tiger Pelt, Snake Venom, Concentrated Venom

To fish

Oyster Clutch, Glass Eel, Marsh Crocodile

The same milieu, otherwise

Mangrove, Corrupted Mangrove, Fungal Mangrove

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