Fontus Lake (Bulgarian: езеро Фонт, romanized: ezero Font, IPA: [ˈɛzɛro ˈfɔnt]) is the oval-shaped 150 m long in south-southwest to north-northeast direction and 100 m wide lake in the middle part of South Beaches on Byers Peninsula, Livingston Island in the South Shetland Islands, Antarctica. It has a surface area of 1.9 ha and is separated from sea by a 53 to 64 m wide strip of land. The area was visited by early 19th century sealers.

The feature is named after Fontus, a Roman deity of springs and streams, son of Juturna.

Fontus Lake is centred at 62°39′40.4″S 61°00′19″W / 62.661222°S 61.00528°W / -62.661222; -61.00528, which is 600 m northeast of Dometa Point and 740 m south of Negro Hill. Detailed Spanish mapping in 1992, and Bulgarian mapping in 2009 and 2017.

• Península Byers, Isla Livingston. Mapa topográfico a escala 1:25000. Madrid: Servicio Geográfico del Ejército, 1992
• 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
• Livingston Island

• Fontus Lake. SCAR Composite Gazetteer of Antarctica
• Bulgarian Antarctic Gazetteer. Antarctic Place-names Commission. (details in Bulgarian, basic data in English)
• J. Ruiz-Fernández and M. Oliva. Relative Paleoenvironmental Adjustments Following Deglaciation of the Byers Peninsula (Livingston Island, Antarctica). Arctic, Antarctic, and Alpine Research 48 (2016) 2. pp. 345-359. (Figure 2: Map of Negro Hill area featuring Fontus Lake)
• Management Plan for Antarctic Specially Protected Area No. 126 Byers Peninsula. Measure 4 (2016), ATCM XXXIX Final Report. Santiago, 2016

• Fontus Lake. Adjusted Copernix satellite image

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