Corrupted Estuary

Nature here has gone sick. Water runs tainted, plants grow in wrong shapes, and the animals are diseased or worse. Whatever lives here eats what it should not. Where a river meets the sea, with mudflats, salt marsh and water that turns from fresh to salt with the tide. Rich in fish and birds, and the natural place for a port.

Hear it

Corrupted: Corrupted Shrine (On Patreon, Raven tier)
Water: Toxic River (On Patreon, Raven tier)
On a barge: Sailing Barge on River (On Patreon, Guardian tier)
A harbour: Cold and Calm Harbor (On Patreon, Raven tier)
Tides: Rough Sea (In the album RPG Ambiences Vol. 8)
Sucking mud: Thorny Swamp (In the album RPG Ambiences Vol. 7)

For the table

Ground: rough, about 20 km a day on foot
Water: plentiful
Foraging: fair

Hazards

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.
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.
Tainted water. The water has a film on it and a sweet smell. Boiling does not make it safe; only clean water carried in does.
Grasping growth. Roots and vines that move when nobody looks. They close around an ankle while the party rests.
Wound rot. Here even a scratch goes black at the edges in a day. Clean cloth and strong drink are worth more than gold.

D&D 5e

Plays as: coastal, normal pace at most
Checks: forage: Survival DC 10 · find the way: DC 5 · search: DC 15
Creatures are spotted at: 2d10 × 10 ft

Tainted water. (House rule) Whoever drinks it makes a DC 13 Constitution save: on a failure, the Poisoned condition until the next long rest and 1 Exhaustion. Purify Food and Drink makes it safe.
Grasping growth. (House rule) A creature resting on the ground makes a DC 12 Dexterity save or has the Restrained condition; escaping takes a DC 12 Strength (Athletics) check or 10 slashing damage dealt to the growth.
Wound rot. (House rule) A creature that took piercing or slashing damage today makes a DC 12 Constitution save at the end of the day, or regains only half the hit points from its next long rest. A healer's kit used on it gives Advantage.

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, difficult terrain, about 16 km a day at Speed 25
Checks: Subsist: Survival DC 10 · Sense Direction: Survival DC 15
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 wants a sample of the sick plants to find a cure. Every sample taken out of the land rots within the hour, unless it is carried by someone who is already sick.
The corruption started at a single spring, and a local lord has paid a priest to say it started elsewhere. The priest is dying of it, and wants to confess before he goes.
A beast of the land has gone strange: a deer with too many legs that is gentle, follows travellers and seems to want help. Following it leads toward the heart of the sickness.
A family that lives on the edge of the corrupted land has learned to eat its plants without falling ill. They will not share the secret, which is that they are no longer entirely human.
The pilot who guides ships past the sandbanks, which shift with every tide, has vanished the night before a fleet is due. His apprentice knows half the channels, and is very honest about which half.
Cockle pickers work the flats at low tide, and the flood comes in faster than a horse can run. A gang master has been sending newcomers out on bad tides, and three of them have drowned this month.
A heron has stood on the same post at the river mouth for thirty years, and sailors say it keeps the port. It has flown away, and the harbour master wants it found before the crews refuse to sail.
The port is silting up and big ships can no longer reach the quays. The rival port across the bay is suspected of dumping ballast in the channel at night, and the guild wants proof, or a quiet reply in kind.

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.
Common Reed (grass). A tall wetland grass of 1.5 to 4 m, found worldwide, that forms vast reed beds in shallow fresh or brackish water, like the 1,700 km² of the Danube Delta. Its purple plumes turn grey and silky in autumn and the stems stand through the winter. It is the classic thatch of Europe. Food of: Goat. Food of: Cattle. Gives: Reed Stem, Reed Rhizome.

Animals

Bottlenose Dolphin (dangerous if cornered, in herds, day and night)
Golden Eagle (dangerous if cornered, in pairs, by day)
Harbour Seal (dangerous if cornered, alone, by day)

Creatures

Dretch (a threat to the unwary, Challenge 1/4)
Quasit (a fight to fear, Challenge 1)
Succubus (a fight to fear, Challenge 4)
Vrock (deadly, Challenge 6)
Glabrezu (deadly, Challenge 9)
Nalfeshnee (deadly, Challenge 13)

Also met here

Giant Crab (a threat to the unwary, Challenge 1/8)
Merrow (a fight to fear, Challenge 2)
Sea Hag (a fight to fear, Challenge 2)
Giant Crocodile (deadly, Challenge 5)
Hydra (deadly, Challenge 8)

To gather

Sea Hag Gill, Wastrilith Acid Venom, Sibriex Bile, Reed Rhizome, Reed Stem, Harbour Seal Blubber, Harbour Seal Pelt, Red Mangrove Bark, Red Mangrove Wood, Golden Eagle Feather, Sunken Ambergris, Enchanted Salt Pinch, Coral Polyp Dust

To fish

Fouled Anchor, Harbour Scrap, Oyster Clutch, Drowned Purse, Glass Eel, Message Bottle, Moonscale Salmon, Sunken Cargo Crate, Marsh Crocodile

The same milieu, otherwise

Estuary, Blessed Estuary, Enchanted Estuary, Toxic Estuary

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