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Soisalo between the lakes Kallavesi, Suvasvesi, Kermajärvi, Ruokovesi, Haukivesi and Unnukka, Finland - 1638 km². Some consider that Soisalo is not a real island because the lakes surrounding it are not on the same level. The greatest difference between the surrounding lakes is 6 m.
Sääminginsalo in Saimaa, Finland - 1069 km² (413 sq miles). Saimaa is sometimes referred to as a "lake system", and Sääminginsalo is surrounded by three separately named lakes (Haukivesi, Puruvesi and Pihlajavesi) that are at the same level, and by an artificial canal, Raikuun kanava, built in 1750's. Since it is detached from land by a canal, it is debatable whether Sääminginsalo can be defined as an island.
Islands of the World: Largest Lake Islands, World Atlas website. Sääminginsalo inserted separately, as it is not featured on the list despite being larger than most other islands in lakes.
