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Sea of Galilee (יָם כִּנֶּרֶת)
Sea of Galilee (Yam Kinneret, Lake Tiberias, Lake Kinneret), Israel's largest freshwater lake in the Jordan Rift Valley, fed by the Jordan River, historically the source of the National Water Carrier and since 2025 refilled with desalinated water.
Sea of Japan (日本海)
Sea of Japan (日本海), also called East Sea: a semi-enclosed Northwest Pacific marginal sea bordered by Japan, Russia, and Korea, area 1.013 million km2, max depth 3,700 m, connected by four shallow straits, a back-arc basin opened from the Eocene, warming faster than the global ocean.
Sea of Marmara
Sea of Marmara (Marmara Denizi), Turkey's inland sea linking Black Sea and Mediterranean via Bosphorus and Dardanelles; lies on North Anatolian Fault with major seismic gap, two-layer Black Sea–Mediterranean water exchange, and 2021 mucilage crisis.
Sea of Okhotsk (Охотское море)
Sea of Okhotsk (Охотское море), a marginal sea of the North Pacific between Siberia, Sakhalin, the Kurils, and Hokkaido; the Southern Hemisphere's northern counterpart in seasonal sea ice, source of North Pacific intermediate water, major pollock fishery, and site of declining ice cover.
Sea of the Hebrides
Sea of the Hebrides: Atlantic sea between Scotland's Inner and Outer Hebrides; also a large Scottish Nature Conservation MPA protecting basking shark, minke whale, fronts, and marine geological features.
Seachannel
A seachannel is an elongated depression on the seabed with a continuously sloping bottom, typically occurring on fans or plains and often flanked by levees.
Seafloor features of the Indian Ocean
The seafloor of the Indian Ocean features an inverted-Y spreading ridge system, the 5,600 km Ninetyeast Ridge, and a deepest point of 7,450 m in the Java Trench.
Seafloor features of the polar oceans
The seafloor features of the polar oceans are the named ridges, basins, plains, and shelves of the Arctic and Southern oceans, whose floors differ sharply from temperate oceans.
Seamount
A seamount, also called an undersea mountain, is an extinct volcano rising at least 1,000 meters from the ocean floor without reaching the surface; flat-topped ones are guyots.
Sebago Lake
Sebago Lake, also called Big Sebago, is Maine's deepest and second-largest lake in Cumberland County, a glacial water supply for over 200,000 in Greater Portland with a filtration exemption, landlocked salmon fishery, and Sebago Lake State Park.
Sebkhet Sidi Elhani
Sebkhet Sidi Elhani (Sebkha Sidi El Hani) is a 36,000 ha intermittently flooded salt lake, or sebkha, in Tunisia's Sahel between Sousse and Mahdia; Ramsar site no. 2019 since 2012 and a BirdLife IBA important for greater flamingo and common crane.
Second Bay
Second Bay: name shared by a bay on Ponui Island in Auckland's Hauraki Gulf, New Zealand (36°53.843′S, 175°12.054′E, a fisheries boundary point), a Coolum Beach reserve in Queensland, a bay in Ontario, Canada, and a bay in Pembrokeshire, Wales.
Second Thomas Shoal
Second Thomas Shoal (Ayungin Shoal; Ren'ai Jiao 仁爱礁) is a low-tide elevation reef in the Spratly Islands, South China Sea, occupied by the Philippines via the grounded warship BRP Sierra Madre since 1999 and contested by China, with a 2024 provisional resupply arrangement.
Segozero
Segozero (Сегозеро, Segojärvi) is a 815 km² lake-reservoir in Karelia, Russia, converted to a reservoir in 1957 by a dam on the Segazha River; deep (103 m), cold, sparsely populated basin with 17 fish species and a large trout farm.
Seine
The Seine is the river of northern France rising on the Langres plateau and flowing through Paris to the English Channel; its 75,000 km² basin, tributaries Yonne, Marne, and Oise, water-quality history, and the 2024–2025 swimmability cleanup distinguish it.
Seizure of Abu Musa and the Greater and Lesser Tunbs
The seizure of Abu Musa and the Greater and Lesser Tunbs was Iran's landing on three Persian Gulf islands on 30 November 1971, claimed by the UAE ever since.
Selenga
Selenga (Селенга), transboundary river of Mongolia and Siberia, largest tributary of Lake Baikal; 1,024 km, 447,000 km² basin, ~30 km³/yr inflow, large Ramsar delta.
Selennyakh
Selennyakh (Селеннях; Yakut Силээннээх), a 796 km left tributary of the Indigirka in Yakutia, Russia, draining 30,800 km² from the Chersky Range through the Moma-Selennyakh Depression and Aby Lowland; mean discharge about 180-220 m³/s, freezes October to May.
Seligman Inlet
Seligman Inlet is an ice-filled inlet on the east coast of Graham Land, Antarctic Peninsula, opening into the Larsen Ice Shelf. Its 972 km² catchment basin drains glaciers from the peninsula's mountain ridge.
Seneca Lake (New York)
Seneca Lake is the largest and deepest of New York's 11 Finger Lakes, a glacial lake about 35 miles long and 200 m deep holding over half the region's water, feeding Geneva's drinking supply and a major wine trail.
Senegal River
The Senegal River (fleuve Sénégal) is a 1,790 km West African river rising in Guinea and flowing to the Atlantic at Saint-Louis; its basin is managed by the 1972 OMVS, whose Diama and Manantali dams supply irrigation, hydropower, and flood control.
Seno Otway
Seno Otway (Seno de Otway) is an inland sea in Chile's Magallanes region, north of the Strait of Magellan, linked to Seno Skyring by Fitz Roy Channel and to the Pacific by Jerónimo Channel; about 80 km long, once a 5,700 km² proglacial lake.
Seno Skyring
Seno Skyring, also called Skyring Sound, is a large semi-enclosed inland sea of about 1,500 km² in Chile's Magallanes region, north of Riesco Island and the Strait of Magellan, discovered by Captain FitzRoy in 1829.
Sepik
Sepik River (Kaiserin Augusta), longest river of Papua New Guinea at 1,126 km, flowing through a largely intact 78,000 km2 basin of 300+ languages; nominated for World Heritage in 2006, threatened by the proposed Frieda River copper-gold mine.
Sesuvium
Sesuvium, sea purslane genus of Aizoaceae; succulent C3/C4/CAM herbs of tropical coasts; S. portulacastrum is an edible facultative halophyte used for sand fixation and saline-soil bioremediation.
Seto Inland Sea (瀬戸内海)
The Seto Inland Sea (瀬戸内海, Setonaikai) is Japan's semi-enclosed sea between Honshu, Shikoku, and Kyushu, about 450 km long, mean depth 38 m, governed since 1973 by a special conservation law and total pollutant load control.
Seven Lakes (Ҳафткӯл) (Tajikistan)
Seven Lakes (Ҳафткӯл, Haft Kul, Marguzor Lakes) is a chain of seven landslide-dammed mountain lakes in the Shing River gorge, Fann Mountains, near Penjikent, Tajikistan, rising from about 1,640 m to 2,400 m.
Severn
Severn names several rivers: the River Severn (Afon Hafren), Britain's longest at 354 km from Plynlimon to the Bristol Channel; a 982 km Ontario river to Hudson Bay; a tidal Maryland river; plus Severn Sound and Township of Severn, Ontario.
Severn Estuary
Severn Estuary (Môr Hafren): funnel-shaped estuary between Wales and England with the world's second-largest tidal range (14 m), a Ramsar site, SPA and SAC supporting 74,000 wintering birds and over 110 fish species.
Severnaya Sosva
Severnaya Sosva (Северная Сосьва), Northern Sosva, an 866-km left tributary of the Ob in KHMAO-Yugra, Russia; Ural-fed whitefish river with endemic tugun, historic Mangazeya trade route, and regulated indigenous fishery.