What people call streams... or brooks... or runs... or something else

If you've done work in rivers in the US, you will quickly learn that names for those flowing bodies of water smaller than a "river" are given different names in different places in the country. Some EFL individuals may think that there is a hierarchical nature to the relationship between a "stream", a "brook", a "run", a "wash", etc. Often, though, there isn't; all these things are similar to each other in that they all mean "a small river" or something akin to that. Looking at the Flowing Data website today, I saw a link to a map by Derek Watkins that lays out the geographic distribution of the various toponyms that describe "small rivers" around the US.

Just to show how similar the definitions for many of these different words are, I present their (relevant) definitions [and etymologies], taken from dictionary.com.

• Branch: a tributary stream or any stream that is not a large river or a bayou; Chiefly South Midland and Southern U.S. branch water.  [1250–1300; Middle English bra (u) nche < Anglo-French; Old French branche &lt; Late Latin branca paw, of uncertain origin]

• Run: a small stream; brook; rivulet. [before 900; (v.) Middle English rinnen, rennen, partly < Old Norse rinna, renna, partly continuing Old English rinnan; cognate with German rinnen; form run orig. past participle, later extended to present tense; (noun and adj.) derivative of the v.]

• Fork: a principal tributary of a river. [before 1000; Middle English forke, Old English forca &lt; Latin furca fork, gallows, yoke]

• Brook: a small, natural stream of fresh water. [before 900; Middle English; Old English brōc stream; cognate with Dutch broek, German Bruch marsh]

• Kill: (US) a channel, stream, or river (chiefly as part of place names) [C17: from Middle Dutch kille; compare Old Norse kīll small bay, creek]

• Stream: a body of water flowing in a channel or watercourse, as a river, rivulet, or brook. [before 900; (noun) Middle English streem, Old English strēam; cognate with German Strom, Old Norse straumr; akin to Greek rheîn to flow (see rheum); (v.) Middle English streamen, derivative of the noun]

• Bayou: a marshy arm, inlet, or outlet of a lake, river, etc., usually sluggish or stagnant; any of various other often boggy and slow-moving or still bodies of water. [1710–20, Americanism < Louisiana French, said to be &lt; Choctaw bayuk river forming part of a delta]

• Swamp: a tract of wet, spongy land, often having a growth of certain types of trees and other vegetation, but unfit for cultivation. [1615–25; < Dutch zwamp creek, fen; akin to sump and to Middle Low German swamp, Old Norse svǫppr sponge]

• Slough: an area of soft, muddy ground; swamp or swamplike region; Also, slew, slue. Northern U.S. and Canadian. a marshy or reedy pool, pond, inlet, backwater, or the like. [before 900; Middle English; Old English slōh; cognate with Middle Low German slōch, Middle High German sluoche ditch]

• Wash: a tract of land washed by the action of the sea or a river; a marsh, fen, or bog; a small stream or shallow pool; a shallow arm of the sea or a shallow part of a river; a depression or channel formed by flowing water; Also called dry wash. Western U.S. the dry bed of an intermittent stream. [before 900; Middle English washen (v.), Old English wascan (cognate with Dutch wasschen, German waschen, Old Norse vaska) < Germanic *watskan, equivalent to *wat- (root of water) + *-sk- v. suffix + *-an infinitive suffix]

• Cañada: Chiefly Western U.S. a dry riverbed; a small, deep canyon. [1840–50;  < Spanish, equivalent to cañ ( a ) cane + -ada noun suffix]

• Arroyo: Chiefly southwest U.S. a small steep-sided watercourse or gulch with a nearly flat floor: usually dry except after heavy rains. [1800–10, Americanism ; < Spanish; akin to Latin arrūgia mine shaft]

• Rio: a river [Spanish rio, from L. rivus "brook, stream"]