The only lake that flows into both the Atlantic and Pacific oceans

Located in Yellowstone National Park between the Old Faithful and West Thumb geyser areas, Lake Isa lies directly on the North American Divide, i.e. the Rocky Mountains. This mountain range runs along North America, separating the river system’s flow to the east and west, emptying into different oceans, according to IFL Science.

As a result of its unique location, the eastern portion of Lake Isa flows into the Lewis River, a tributary of the Columbia River, which flows into the Pacific Ocean. Meanwhile, the western part of this lake flows into the Firehole River, a tributary of the Madison River, which flows into the Gulf of Mexico, connecting to the Atlantic Ocean through the Florida Straits.

Lake Isa is located on a pass at an altitude of 2,518 m. In the spring, when there is runoff due to melting snow, lake water will move in two directions. Because Lake Isa is located in a basin, it only flows into the sea when the water level is high enough. During many recent winters, Yellowstone’s snow was not deep enough to fill the lake. That turns Isa into a closed lake, with water flowing in but not flowing out. For most of the year, the water in Lake Isa does not flow into the two oceans but evaporates under the hot sun.

A similar phenomenon occurred at the much larger Ladoga Lake located near St Petersberg in northwestern Russia, close to the Finnish border. Most of the lake flows into the Gulf of Finland via the Neva River, eventually reaching the Baltic Sea. However, the lake also connects with tributaries of the Volga river system, flowing into the Caspian Sea.

Another example is the Nerodime River in southern Kosovo. Located on the outskirts of Ferizaj city, the river splits into two paths, called bifurcations. The left branch flows into the Black Sea while the right branch flows into the Aegean Sea, making it the only river in Europe that flows into two seas.