There's a Hole in Mozambique

Here's an interesting close-up of the triple-border between Malawi, Mozambique, and Tanzania on Lake Nyasa (aka Lake Malawi). The two islands in the rounded enclave are Chisamula (the small one) and Likoma -- they belong to Malawi but are surrounded by Mozambiquan waters. I wonder if there's anywhere else in the world with such a perfec elipse of a border.

Also, it's interesting that whereas Malawi and Mozambique roughly split the southern end of the lake, up north Tanzania border hugs its own shoreline, giving Malawi all the water.