Its two nearly-separate s
Its two nearly-separate sub-basins are connected by the Strait of Tiquina, and its single outlet, Rio Desaguadero, flows through the smaller of these sub-basins, Lago Huiñaimarca.  Inside lies the island of Isla del Sol which features many Incan ruins.  Located in the Andes mountains, it is about halfway between La Paz and and Arequipa, It is over 170 kilometers long and 4000 meters above sea level.  For 10 points, what is this lake that sits on the border between Bolivia and Peru?
Its two nearly-separate sub-basins are connected by the Strait of Tiquina, and its single outlet, Rio Desaguadero, flows through the smaller of these sub-basins, Lago Huiñaimarca.  
ANSWER: Lake {Titicaca}