A recursive island or lake, also known as a nested island or lake, is an island that lies inside a lake, or vice versa. For the purposes of defining recursion, small continental land masses such as Madagascar and New Zealand count as islands, while large continental land masses such as Australia do not. Islands found within lakes in these countries are often recursive islands because the lake itself is located on an island.
There are nearly 1,000 islands in lakes on islands in Finland alone.