Estuary

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

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: rich

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.

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

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.

Crossing it

Besides walking, depending on the era and the season (Biomes estimates of a day’s distance):

On horseback: about 30 km a day
By river boat: about 40 km a day
By train: about 400 km a day
By airship: about 900 km a day
By bush plane: about 800 km a day
By 4x4: about 100 km a day
By rover: about 60 km a day
By hover sled: about 100 km a day
On a flying mount: about 150 km a day
By flying carpet: about 100 km a day
By car: about 200 km a day
By truck: about 150 km a day
By motorbike: about 150 km a day
By armoured buggy: about 120 km a day

Adventure hooks

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

Blind-your-eye Mangrove (tree). A mangrove tree up to 15 m of salt and brackish water, from India and Bangladesh to South China and Australia, growing at the back of the swamp where the water is least salty. Its milky latex blisters the skin, and a drop in the eye blinds for a time: Cook's men were blinded cutting it for wood, and Bligh forbade his crew to cut it in 1789, for even the smoke of the burning wood hurts the eyes. Gives: Blind-Your-Eye Latex.
Cannonball Mangrove (tree). A common evergreen mangrove of the mahogany family, from Kenya and Mozambique to India, Southeast Asia, northern Australia and the Pacific islands, growing high in the intertidal zone, in estuaries and along creeks. Its buttressed trunk sends roots far to either side, and it bears woody balls 9 to 12 cm across that split into a dozen odd-shaped seeds, which give it its other name, the puzzlenut tree. Gives: Cannonball Mangrove Wood, Cannonball Mangrove Bark.
Grey Mangrove (tree). A mangrove tree of 3 to 10 m (up to 14 m in the tropics) that sheds salt through its leaves and breathes through pencil-like roots poking out of the mud at low tide. It lines mudflats, sandy shores and estuaries around the Indian Ocean, from East Africa and Arabia to Australia and northern New Zealand, even on desert coasts. Its heavy, durable wood makes poles and boat ribs, and the smoke of the burning wood keeps mosquitoes off. Gives: Grey Mangrove Wood, Grey Mangrove Seedlings.
Mangrove Apple (tree). A mangrove tree up to 20 m tall, ringed by cone-shaped breathing roots up to 2 m high, growing on tidal mudflats and creeks from South Asia to northern Australia and the Pacific islands. Its round, sour fruit tastes faintly of cheese and is eaten raw, cooked as a vegetable or mixed into drinks. Fishermen cut the roots into net floats, and fireflies gather in it. Gives: Mangrove Apple, Mangrove Apple Wood.
Nipa Palm (tree). A palm with no trunk above ground: its stem creeps through the mud and only the fronds, up to 9 m long, rise from it. It grows in soft mud along tidal rivers and mangroves from India and Sri Lanka through Southeast Asia to New Guinea and northern Australia. Its sweet sap makes palm wine, vinegar and sugar, its young seeds are a sweet snack, and its fronds make excellent thatch, longer-lasting than coconut thatch. Food of: Crab-eating Macaque. Gives: Nipa Palm Sap, Nipa Palm Seeds, Nipa Palm Frond.
Large-leafed Orange Mangrove (tree). A mangrove tree of 7 to 20 m with bright red flowers and knee-like roots, growing on the landward side of mangroves along the Indian and Pacific oceans, from South Africa to the western Pacific. Its long seedlings are full of starch: peeled and boiled in several changes of water to drive out the bitter tannin, they are a staple for the Sowek people of Papua. The bark tans leather and dyes cloth red-brown to black, and the dense wood makes posts and charcoal. Gives: Orange Mangrove Seedling, Orange Mangrove Bark, Orange Mangrove Wood.
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.
White Mangrove (tree). A mangrove tree with grey-brown or reddish fissured bark and thick, yellow-green leaves, on the coasts of West Africa from Senegal to Cameroon and on the Atlantic and Pacific coasts of the Americas, the Galápagos included. It grows in bays, lagoons and tidal creeks, usually inland of the other mangroves and well above the high-tide line; two small glands at the base of each leaf ooze sugar.
Sea Purslane (shrub). A shrub up to 1 m tall of the sea shores of western and southern Europe and from the Mediterranean to western Asia, with thick, oval, powdery leaves, growing in salt marshes and coastal dunes and usually flooded at high tide. Gives: Sea Purslane Leaves.
Glasswort (herb). A small succulent annual, 20 to 30 cm, with jointed stems so full of water they look almost translucent, which gave it the name glasswort, and leaves reduced to scales; it grows in salt marshes, on beaches and among mangroves on most coasts of Europe. Eaten as marsh samphire: young shoots raw in May and June, later boiled in plenty of unsalted water; it tastes of young spinach stems, asparagus or artichoke. Its ash long gave the alkali of glassmakers and soapmakers, and the word alkali comes from the Arabic al-qalyah, 'glasswort ash'. Gives: Marsh Samphire.
Sea Aster (herb). A perennial of up to 50 cm with fleshy leaves and purple, blue or white rays around a yellow heart, native to Eurasia and North Africa and confined to salt marshes, estuaries and the odd inland salt works. It flowers from July well into autumn, a late feast for butterflies such as the painted lady and red admiral. Gives: Sea Aster Leaves.
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.
Eelgrass (grass). The most widespread seagrass of the northern hemisphere, with ribbon leaves up to over a metre long, growing on sand and mud below the low spring tides in bays, lagoons and estuaries of the North Atlantic and North Pacific, as far as Iceland and under months of Arctic ice. Its meadows shelter herring spawn and young cod and feed brant geese, and when it washes ashore it feeds a whole world of sand-hoppers, flies and beetles; a wasting disease in the 1930s killed much of it. It roofed houses on Læsø in Denmark, fed cattle in Norway and stuffed mattresses, and the Seri of Mexico toasted and ground its grains. Gives: Dried Eelgrass.
Smooth Cordgrass (grass). The grass of the estuarine salt marshes of the Atlantic coast of the Americas, from Newfoundland to northern Argentina, called the single most important marsh plant of the Chesapeake Bay. It grows out into the water at the marsh's seaward edge and traps mud there, so the marsh creeps seaward behind it. Brought elsewhere, it smothers mudflats: China planted it for shore protection from 1979 and it now covers over 34,000 hectares there.
Knotted Wrack (seaweed). A large brown seaweed of the cold North Atlantic, from the White Sea to Portugal and from east Greenland to Long Island, with tough fronds up to 2 m long strung with egg-shaped air bladders, one added each year, and living 10 to 15 years. It dominates the middle of sheltered shores and estuaries, and its mats shelter barnacles, periwinkles and more than a hundred other species. Ireland has cut it for centuries, at low tide with a knife or sickle; it goes into alginates, fertiliser and seaweed meal for beasts and people, Greenlanders take it as a food supplement, and New England ships live bait and lobsters packed in it. Gives: Knotted Wrack.
Sea Lettuce (seaweed). A thin bright green seaweed found on coasts all over the world, fixed to rocks, jetties, shells and other algae from the upper shore down to about 10 m, and most abundant where the water is rich in nutrients. It is eaten raw or cooked: in soups and salads in Scotland, salted with raw fish or boiled as soup in Hawaii; it also serves as fertiliser. Piles of it rotting on the shore give off toxic hydrogen sulphide, as in Brittany in 2009. Gives: Sea Lettuce.

Animals

Saltwater Crocodile (man-killer, alone, day and night)
Bottlenose Dolphin (dangerous if cornered, in herds, day and night)
Common Snapping Turtle (dangerous if cornered, alone, by day)
Golden Eagle (dangerous if cornered, in pairs, by day)
Harbour Seal (dangerous if cornered, alone, by day)
Mud Crab (dangerous if cornered, alone, day and night)
Mute Swan (dangerous if cornered, in pairs, by day)
Common Cockle (harmless, in colonies, day and night)
Common Periwinkle (harmless, in colonies, day and night)
Grey Heron (harmless, alone, at dawn and dusk)
Greylag Goose (harmless, in flocks, by day)
Hawksbill Sea Turtle (harmless, alone, by day)
Loggerhead Sea Turtle (harmless, alone, by day)
Mallard (harmless, in flocks, by day)
Sandfish (harmless, alone, by night)
Scarlet Ibis (harmless, in colonies, by day)

Creatures

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

Cannonball Mangrove Bark, Cannonball Mangrove Wood, Cockles, Periwinkles, Reed Rhizome, Reed Stem, Snapping Turtle Meat, Dried Eelgrass, Marsh Samphire, Grey Mangrove Seedlings, Grey Mangrove Wood, Greylag Goose Egg, Greylag Goose Feathers, Greylag Goose Meat, Harbour Seal Blubber, Harbour Seal Pelt, Knotted Wrack, Loggerhead Turtle Meat, Mallard Meat, Mangrove Apple, Mangrove Apple Wood, Mud Crab Meat, Nipa Palm Frond, Nipa Palm Sap, Nipa Palm Seeds, Orange Mangrove Bark, Orange Mangrove Seedling, Orange Mangrove Wood, Red Mangrove Bark, Red Mangrove Wood, Saltwater Crocodile Meat, Scarlet Ibis Egg, Sea Aster Leaves, Sea Lettuce, Sea Purslane Leaves, Blind-Your-Eye Latex, Golden Eagle Feather, Grey Heron Meat, Mute Swan Feather, Mute Swan Meat, Saltwater Crocodile Hide, Trepang, Scarlet Ibis Feather, Tortoiseshell, Sunken Ambergris, Enchanted Salt Pinch, Coral Polyp Dust

Fantasy variants

Blessed Estuary, Corrupted Estuary, Enchanted Estuary, Toxic Estuary

Nearby biomes

Rocky Shore, Sandy Shore

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