The area is drained by the river Bečvou, which flows into the River Morava. With heavy rain the river can flood. The most devastating floods in Moravia were 5–16 July 1997. The flood water got into the cave, including the Marble Hall. At the same time the levels of mineral pools was raised and carbon dioxide gas reached the higher level caves. The gas in the visitor area was solved by installing a special suction device that keeps the composition of the air in the values ​​set by the State Mining Administration (up to 1% CO2). The floods also damaged much of the technical equipment, but did not damage the cave's natural features.