Bay mud in the context of Penobscot Bay

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word βένθος (bénthos), meaning "the depths". Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi) as well as larger invertebrates, such as crustaceans and polychaetes.

Organisms here, known as bottom dwellers, generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal flat ecosystems are as extensive globally as mangroves, covering at least 127,921 km (49,391 sq mi) of the Earth's surface. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries; they are also seen in freshwater lakes and salty lakes (or inland seas) alike, wherein many rivers and creeks end. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and aquatic animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

A recent global remote sensing analysis estimated that approximately 50% of the global extent of tidal flats occurs within eight countries (Indonesia, China, Australia, United States, Canada, India, Brazil, and Myanmar) and that 44% of the world's tidal flats occur within Asia (56,051 km or 21,641 sq mi). A 2022 analysis of tidal wetland losses and gains estimates that global tidal flats experienced losses of 7,000 km (2,700 sq mi) between 1999 and 2019, which were largely offset by global gains of 6,700 km (2,600 sq mi) over the same time period.

Mud (from Middle Low German mudde, mod(de) 'thick mud', or Middle Dutch) is loam, silt or clay mixed with water. Mud is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone (generally called lutites). When geological deposits of mud are formed in estuaries, the resultant layers are termed bay muds. Mud has also been used for centuries as a construction resource for mostly houses and also used as a binder. An Old English word for it was fen, now in most dialects referring to a type of wetland.

Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal flat ecosystems are as extensive globally as mangroves, covering at least 127,921 km (49,391 mi) of the Earth's surface. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries; they are also seen in freshwater lakes and salty lakes (or inland seas) alike, wherein many rivers and creeks end. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and aquatic animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

A recent global remote sensing analysis estimated that approximately 50% of the global extent of tidal flats occurs within eight countries (Indonesia, China, Australia, United States, Canada, India, Brazil, and Myanmar) and that 44% of the world's tidal flats occur within Asia (56,051 km or 21,641 mi). A 2022 analysis of tidal wetland losses and gains estimates that global tidal flats experienced losses of 7,000 km (2,700 mi) between 1999 and 2019, which were largely offset by global gains of 6,700 km (2,600 mi) over the same time period.