Lake Sevan () is the largest body of water in both Armenia and the Caucasus region. It is one of the largest freshwater high-altitude (alpine) lakes in Eurasia. The lake is situated in Gegharkunik Province, at an altitude of above sea level. The total surface area of its basin is about , which makes up of Armenia's territory. The lake itself is , and the volume is . It is fed by 28 rivers and streams. Only 10% of the incoming water is drained by the Hrazdan River, while the remaining 90% evaporates. The lake provides some 90% of the fish and 80% of the crayfish catch of Armenia. Sevan has significant economic, cultural, and recreational value. Its sole major island (now a peninsula) is home to a medieval monastery. Sevan was heavily exploited for irrigation of the Ararat plain and hydroelectric power generation during the Soviet period. Consequently, its water level decreased by around and its volume reduced by more than 40%. Later two tunnels were built to divert water from highland rivers, which halted its decline and its level began rising. Before human intervention dramatically changed the lake's ecosystem, the lake was at an altitude of above sea level, deep, covered an area of (5% of Armenia's entire area), and had a volume of . Etymology Scholars believe that Sevan originated from the Urartian word su(i)n(i)a, usually translated as "lake". The word is found on an 8th-century BC cuneiform inscription by the Urartian king Rusa I, found in Odzaberd, on the southern shore of the lake. Per folk etymology, Sevan is either a combination of sev ("black") + Van (i.e., Lake Van) or sev ("black") and vank’ ("monastery"). Russian and European sources of the 19th and early 20th century sometimes referred to the lake as Sevanga or Sevang, which are likely the Russified version of the Armenian phrase sev vank’ ("black monastery") or, possibly, the Armenian phrase սա է վանքը sa ē vank'ə ("this is the monastery"). The historical Armenian name of the lake, attested in early medieval texts, is Sea of Gegham (classical Armenian: ծով Գեղամայ, tsov Geghamay). In classical antiquity, the lake was known as Lychnitis (). The historic Georgian name of the lake is Gelakuni (გელაქუნი), which is essentially the Georgian transcription of Armenian Gegkarkuni. John Chardin, who visited the lake in 1673, called it the "Lake of Erivan" and wrote that it was called