Ice age and retreating glaciers created holes. And those holes filled up by the melt water of the glaciers.
The fact that they are still full of water is due to them being replenished by precipitation more than they lose water. If they would lose more water then what flows into them we would be speaking about the "land of many bone dry holes" in the famous Finnish desert.
The fact that they are still full of water is due to them being replenished by precipitation more than they lose water. If they would lose more water then what flows into them we would be speaking about the "land of many bone dry holes" in the famous Finnish desert.