The main difference between Sea and River is that the Sea is a large body of saline water and River is a natural watercourse.
A sea is a large body of salt water that is surrounded in whole or in part by land. More broadly, “the sea” is the interconnected system of Earth’s salty, oceanic waters—considered as one global ocean or as several principal oceanic divisions. The sea moderates Earth’s climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. Although the sea has been traveled and explored since prehistory, the modern scientific study of the sea—oceanography—dates broadly to the British Challenger expedition of the 1870s. The sea is conventionally divided into up to five large oceanic sections—including the International Hydrographic Organization’s four named oceans (the Atlantic, Pacific, Indian, and Arctic) and the Southern Ocean; smaller, second-order sections, such as the Mediterranean, are known as seas.
Owing to the present state of continental drift, the Northern Hemisphere is now fairly equally divided between land and sea (a ratio of about 2:3) but the South is overwhelmingly oceanic (1:4.7). Salinity in the open ocean is generally in a narrow band around 3.5% by mass, although this can vary in more landlocked waters, near the mouths of large rivers, or at great depths. About 85% of the solids in the open sea are sodium chloride. Deep-sea currents are produced by differences in salinity and temperature. Surface currents are formed by the friction of waves produced by the wind and by tides, the changes in local sea level produced by the gravity of the Moon and Sun. The direction of all of these is governed by surface and submarine land masses and by the rotation of the Earth (the Coriolis effect).
Former changes in sea levels have left continental shelves, shallow areas in the sea close to land. These nutrient-rich waters teem with life, which provide humans with substantial supplies of food—mainly fish, but also shellfish, mammals, and seaweed—which are both harvested in the wild and farmed. The most diverse areas surround great tropical coral reefs. Whaling in the deep sea was once common but whales’ dwindling numbers prompted international conservation efforts and finally a moratorium on most commercial hunting. Oceanography has established that not all life is restricted to the sunlit surface waters: even under enormous depths and pressures, nutrients streaming from hydrothermal vents support their own unique ecosystem. Life may have started there and aquatic microbial mats are generally credited with the oxygenation of Earth’s atmosphere; both plants and animals first evolved in the sea.
The sea is an essential aspect of human trade, travel, mineral extraction, and power generation. This has also made it essential to warfare and left major cities exposed to earthquakes and volcanoes from nearby faults; powerful tsunami waves; and hurricanes, typhoons, and cyclones produced in the tropics. This importance and duality has affected human culture, from early sea gods to the epic poetry of Homer to the changes induced by the Columbian Exchange, from burial at sea to Basho’s haikus to hyperrealist marine art, and inspiring music ranging from the shanties in The Complaynt of Scotland to Rimsky-Korsakov’s “The Sea and Sinbad’s Ship” to A-mei’s “Listen to the Sea”. It is the scene of leisure activities including swimming, diving, surfing, and sailing. However, population growth, industrialization, and intensive farming have all contributed to present-day marine pollution. Atmospheric carbon dioxide is being absorbed in increasing amounts, lowering its pH in a process known as ocean acidification. The shared nature of the sea has made overfishing an increasing problem.
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are “run” in some parts of the United States, “burn” in Scotland and northeast England, and “beck” in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.Rivers are part of the hydrological cycle; water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, and as a means of disposing of waste.
A large body of salt water.
The ocean; the continuous body of salt water covering a majority of the Earth’s surface.
A lake, especially if large or if salty or brackish.
“The Caspian Sea, the Sea of Galilee, the Salton Sea, etc.”
The swell of the sea; a single wave; billow.
Living or used in or on the sea; of, near, or like the sea.
“Seaman, sea gauge, sea monster, sea horse, sea level, seaworthy, seaport, seaboard, etc.”
Anything resembling the vastness of the sea.
A large, dark plain of rock; a mare.
“The Apollo 11 mission landed in the Sea of Tranquility.”
A very large lake of liquid hydrocarbon.
A large and often winding stream which drains a land mass, carrying water down from higher areas to a lower point, ending at an ocean or in an inland sea.
“Occasionally rivers overflow their banks and cause floods.”
Any large flow of a liquid in a single body.
“a river of blood”
The last card dealt in a hand.
A visually undesirable effect of white space running down a page, caused by spaces between words on consecutive lines happening to coincide.
One who rives or splits.
To improve one’s hand to beat another player on the final card in a poker game.
“Johnny rivered me by drawing that ace of spades.”
a large natural stream of water flowing in a channel to the sea, a lake, or another river
“the Mekong River”
“the River Danube”
a large quantity of a flowing substance
“great rivers of molten lava”
used in names of animals and plants living in or associated with rivers, e.g. river dolphin.