Final answer:
Lake Titicaca is the highest navigable lake in the world, composed of two nearly separated sub-basins.
Step-by-step explanation:
The highest navigable lake in the world, composed of two nearly separated sub-basins, is Lake Titicaca located in the Andes Mountains on the border of Bolivia and Peru.
At an elevation of approximately 3,812 meters (12,507 feet) above sea level, it is the largest lake in South America by volume and the highest navigable lake globally.