Lakes

Water is common in the Upperdark, since runoff from the surface frequently drains into cave systems belowground. In many areas, the water table is close enough to the surface that only the most shallow cave systems can form. However, due to the unusual factors involved in the creation of Underdark, a water table 20 feet belowground does not necessarily mean that air-filled caves don’t exist at greater depths.

A body of fresh water is called a lake. Underdark lakes range in size from small pools to inland seas hundreds of miles in extent. Large lakes typically occupy either tremendous vaults or connected networks of partially submerged caves. The Lagoon of Darkness and the Titan’s Goblet are examples of the former type, and there are many examples of the latter. If a lake has both an inlet and an outlet, its water is usually drinkable, but lakes that are not refreshed from time to time may stagnate.

Most lakes are found in the Upper-Dark or Mid-Dark. Bodies of water that collect in the Lower-Dark simply can’t drain to any lower elevations, so they tend to be seas of salty water instead. However, a few of the bodies of water in the Lower-Dark hold fresh water.

Large lakes can form the best and most accessible highways of the Underdark. In many places, however, the cavern ceiling descends to meet the water, making the lake impassable to all but aquatic creatures.