Lake Arpi (Armenian: Արփի լիճ) is located in the Shirak Province of Armenia, in the northwestern part of the country. The lake level is at an altitude of 2,023 m. The lake area is 22 square kilometres. The area was increased artificially in the 1950s from the natural state of 4.5 square kilometres, and the lake has become the second most important water body of Armenia, next to Lake Sevan. It is used for irrigation and hydropower production. The lake is fed by meltwater and four streams, and it is the source of the Akhurian River.
The lake has rich flora and fauna. It is a Ramsar Convention protected site, and a national park was established around the lake in 2009. More than 100 species of birds have been observed around Lake Arpi.