Proteus Lake (Bulgarian: езеро Протей, romanized: ezero Protey, IPA: [ˈɛzɛro proˈtɛj]) is the roughly pentagonal lake extending 300 m in west–east direction and 220 m in south–north direction in the central part of Flamingo Beach on the north coast of Greenwich Island in the South Shetland Islands, Antarctica. It has a surface area of 3.9 ha and is separated from the waters of Orión Passage by a 20 to 35 m wide strip of land. The area was visited by early 19th century sealers.

The feature is named after the water deity Proteus in Greek mythology.

Proteus Lake is situated at the base of Brusen Point and centred at 62°26′36″S 59°48′24″W / 62.44333°S 59.80667°W / -62.44333; -59.80667, which is 1.42 km east-northeast of Terimer Point and 900 m west-southwest of Agüedo Point. Bulgarian mapping of the area in 2009 and 2017.

• L. Ivanov. Antarctica: Livingston Island and Greenwich, Robert, Snow and Smith Islands. Scale 1:120000 topographic map. Troyan: Manfred Wörner Foundation, 2009. ISBN 978-954-92032-6-4
• L. Ivanov. Antarctica: Livingston Island and Smith Island. Scale 1:100000 topographic map. Manfred Wörner Foundation, 2017. ISBN 978-619-90008-3-0
• Antarctic Digital Database (ADD). Scale 1:250000 topographic map of Antarctica. Scientific Committee on Antarctic Research (SCAR). Since 1993, regularly upgraded and updated

• Antarctic lakes

• Proteus Lake. SCAR Composite Gazetteer of Antarctica
• Bulgarian Antarctic Gazetteer. Antarctic Place-names Commission. (details in Bulgarian, basic data in English)

• Proteus Lake. Adjusted Copernix satellite image

This article includes information from the Antarctic Place-names Commission of Bulgaria which is used with permission.