An underground river
This sapphire-colored pool in the Cayo District is a geological feature known as a karst window. It is an exposed segment of a subterranean river, showing the underground drainage systems that riddle the limestone bedrock of Belize. The feature was created when the roof of a cavern in an underground river system collapsed, unroofing a portion of the channel. This specific karst window is part of St. Herman's Blue Hole National Park, a protected area of over 500 acres.
The water in the Blue Hole is part of a larger network. An underground branch of the Sibun River flows through the extensive St. Herman's Cave system, disappears beneath the surface, and reemerges in this tranquil pool before vanishing once more into the limestone underworld. This process is characteristic of karst topography, a landscape formed by the dissolution of soluble rocks like limestone. The constant flow of slightly acidic water carves and enlarges subterranean passages over millennia, creating vast networks of caves and underground rivers.