I have visited an island in a lake before in Nicaragua well Colombia have theirs too.
Pasto is the main reason to visit the area and this makes a pleasant day trip. Pasto is the logical hub for entering Ecuador. The local delicasy of cuy is guinea pig ! Trout is farmed in the lago and may also be on the menu.
Rio Encano is the river feeding into this amazing lake and here there are numerous restaurants here. The island is a national park and there are collectivo boats taking you to the island.