Waters and hydrographic features

Sistema de Humedales de la Zona Sur de Honduras

Sistema de Humedales de la Zona Sur de Honduras, Ramsar site no. 1000: seven coastal wetland areas on the Golfo de Fonseca (Choluteca and Valle), designated 10 July 1999, 69,711 ha extended to 75,031.13 ha, mangrove ecosystem threatened by shrimp aquaculture.

Sistema Delta Estuarino del Río Magdalena, Ciénaga Grande de Santa Marta

Sistema Delta Estuarino del Río Magdalena, Ciénaga Grande de Santa Marta (SDERM CGSM): Colombia's largest coastal lagoon and first Ramsar site (1998, site 951), a Caribbean brackish wetland hit by causeway-driven mangrove die-off, partially rehabilitated by 1990s dredging, and invaded by Hydrilla verticillata in 2025.

Sistema Hidrológico de Soncor del Salar de Atacama

Sistema Hidrológico de Soncor del Salar de Atacama, Ramsar Site 876 (designated 2 December 1996, 67,133 ha), is a Chilean high-Andean wetland of shallow saline lagoons (Puilar, Chaxa, Barros Negros) fed by eastern groundwater, a key breeding site for three flamingo species within Los Flamencos National Reserve.

Sistema Lagunar Agiabampo - Bacorehuis - Río Fuerte Antiguo

Sistema Lagunar Agiabampo-Bacorehuis-Río Fuerte Antiguo, Ramsar site 1797, is a 90,804 ha five-lagoon coastal wetland on the Sonora-Sinaloa border, Gulf of California, designated 2 February 2008, with mangroves, migratory birds, and blue shrimp habitat.

Sitang - Irawaddy

Sitang - Irawaddy (FEOW ecoregion 720) is a freshwater ecoregion covering Myanmar's Sittang and Ayeyarwady (Irrawaddy) basins, a tropical floodplain-river habitat with 62 recorded endemic fish species and the critically endangered Ayeyarwady Irrawaddy dolphin.

Site of Special Scientific Interest

Site of Special Scientific Interest (SSSI): UK designation for land of special flora, fauna, or geological interest, notified by Natural England under the Wildlife and Countryside Act 1981; 4,127 English sites covering 1,088,000 hectares, with condition targets to 2042.

Skadar

Lake Skadar (Shkodra, Skadarsko jezero) is the largest lake in the Balkans, on the Montenegro-Albania border: shallow karst cryptodepression, 44 km long, Morača-fed, national park since 1983, Ramsar site, declining water levels.

Skagerrak

Skagerrak: deep arm of the North Sea between Norway, Sweden, and Denmark, bounded by Hanstholm–Lindesnes and Skagen–Pater Noster; about 32,000 km², up to 700 m deep in the Norwegian Trench, with cyclonic circulation and Baltic outflow.

Skeena

Skeena (Skeena River, Tsimshian K'shian), British Columbia's second-largest river, flows about 580 km from northwestern BC to Chatham Sound near Prince Rupert; a major salmon and steelhead watershed with 66 salmon Conservation Units.

Skookumchuck Narrows

Skookumchuck Narrows (stl'ikwu), a tidal narrows near Egmont, BC, joins Sechelt Inlet to Jervis Inlet; its Sechelt Rapids run up to 16–17 knots over a 5 m sill, moving 200 billion gallons per three-metre tide.

Smith Inlet (inlet)

Smith Inlet: ice-filled inlet, 15 mi long, between Cape Boggs and Cape Collier on the east coast of Palmer Land, Antarctica; discovered by USAS in 1940, once mislabeled Stefansson Inlet, named for Rear Admiral Edward H. Smith, USCG.

Smith Sound

Smith Sound: channel at the northern end of Baffin Bay between Ellesmere Island and Greenland, southernmost part of Nares Strait leading to Kane Basin; explored by Kane, Hayes, Hall, and Nares; site of gap winds and the North Water polynya.

Smoothstone Lake

Smoothstone Lake is a large, lightly accessed lake in central Saskatchewan, Canada, about 68,959 acres with a 96 km shoreline, a provincial recreation site, and a year-round fishing and hunting lodge.

Snake River

Snake River, largest tributary of the Columbia River, rises in Yellowstone's Two Ocean Plateau, flows through Wyoming, Idaho, and Washington. Named for the Shoshone by 1812; 22 dams, four contested lower-Snake dams, and threatened salmon define it.

Snoqualmie Falls

Snoqualmie Falls is a 270-foot waterfall on the Snoqualmie River in Snoqualmie, Washington, about 30 miles east of Seattle, drawing about 2 million visitors a year.

Society of Wetland Scientists

Society of Wetland Scientists (SWS), international professional society founded 1980 by Richard Macomber; 3,000+ members in 60+ countries; publishes Wetlands journal and Wetland Science & Practice; administers PWS certification.

Socotra

Socotra (سقطرى), Yemeni archipelago in the northwest Indian Ocean near the Gulf of Aden; UNESCO Natural World Heritage Site 2008 with 37% endemic plants, 90% endemic reptiles, 95% endemic land snails, dragon's blood trees, and threats from goats, cyclones, and Yemen's civil war.

Soda geyser

A soda geyser, also called a Mentos and coke geyser, is a fountain of carbonated liquid produced when dissolved carbon dioxide erupts from a soda, famously after Mentos candy is dropped in.

Soda lake

Soda lake (alkaline lake): a closed-basin lake dominated by sodium carbonates, typically pH 9–12 and often hypersaline. Examples include Lake Van, Mono Lake, and Lake Magadi; habitats of haloalkaliphilic microbes and sources of soda ash.

Sognefjord

Sognefjord (Sognefjorden), Norway's longest and deepest fjord at 205 km and about 1,308 m, runs from Solund to Skjolden; second longest worldwide after Scoresby Sound, with the UNESCO-listed Nærøyfjord arm.

Oct 15, 2026

Soil and Water Assessment Tool

The Soil and Water Assessment Tool, or SWAT, is a public-domain watershed model that predicts how management decisions affect water, sediment, nutrient, and pesticide yields.

Sokoto (landform)

Sokoto (landform): the Sokoto River, a left-bank tributary of the Niger in semi-arid northwestern Nigeria, and the Sokoto Plains; 193,000 km2 Sokoto-Rima basin, 700 to 900 mm rain, Bakolori and Goronyo dams, shrinking floodplain.

Solberg Inlet

Solberg Inlet (索爾伯格灣), Antarctic Peninsula inlet, ice-filled, 5-10 nmi wide, receding west 14 nmi between Rock Pile Peaks and Joerg Peninsula on the east coast of Graham Land, near 68.3°S 65.2°W.

Solomon Archipelago

Solomon Archipelago: marine ecoregion (MEOW, Eastern Coral Triangle province) spanning a 1,500 km arc from Bougainville to San Cristobal, with 516 coral species, Ontong Java atolls, Marovo Lagoon, and East Rennell World Heritage site.

Solomon Sea

Solomon Sea: marginal sea of the southwest Pacific between eastern Papua New Guinea and the Solomon Islands, part of the Coral Sea, about 720,000 sq km; main pathway carrying roughly 20 Sv of South Pacific water to the equator.

Solti-síkság

Solti-síkság (Solt Plain, also Csepel-Solt-Bajaisíkság, Kalocsai-síkság) is a Hungarian geographical microregion (code 1.1.22) on the Danube's left bank in Bács-Kiskun County, a 93 m floodplain with saline soils and 99.2 D-e-Meter cropland quality.

Solway Firth

Solway Firth: mega-tidal estuary of the Irish Sea between Dumfries and Galloway, Scotland, and Cumbria, England; carries the Anglo-Scottish border via the River Sark, has the UK's second largest tidal range, and holds the 436 km² Upper Solway Ramsar site and Solway Firth SAC.

Somali Current

Somali Current: seasonally reversing western boundary current of the Indian Ocean off East Africa, flowing northeast in the southwest monsoon at up to 3 m/s, reversing in winter, and driving the world's strongest seasonal coastal upwelling with the Great Whirl eddy.

Somerset Levels

The Somerset Levels are a low-lying, drained wetland plain of about 650 km2 in southwest England, home of the Neolithic Sweet Track, rich wetland wildlife, and extensive flood management infrastructure.