An Islandlake (German Inselsee ) is a lake within an island. One can take this as an example of an iteration, as in mathematics.

Geographical famous examples are "Danau " (Indonesian for lake) Toba on Sumatra, lake Biwa on Honshu, and the lakes and lochs of Great Britain, Ireland, and New Zealand.

The iteration can be carried still further, of course. There are islands within many islandlakes, and occasionally some of these will have small lakes on them.