The lake is situated in the valley of the Chagres River. It was formed, and the river widened and deepened, by the construction of the Gatun Dam about 10 km (6.2 mi) from the river’s mouth in the Caribbean Sea in 1907–1913. The geography of the area was ideal for the creation of a large lake here; the hills bordering the valley of the Chagres open up widely around the area of the lake, but come together to form a gap just over 2 km (1.2 mi) wide at the location of the dam. The damming of the river flooded the originally wooded valley; almost a century later, the stumps of old mahogany trees can still be seen rising from the water, and submerged snags form a hazard for any small vessels that wander off the marked channels.
“The lake was created between 1907 and 1913 by the building of the Gatun Dam”