Crater lakes are bodies of water that form in the depressions left by volcanic activity. When a volcano erupts, it can create a large crater, which may fill with rainwater or meltwater over time. These lakes can vary in size and depth, often featuring unique ecosystems due to their isolated nature. Many crater lakes are known for their striking blue or green colors, which result from minerals and algae in the water. Some famous examples include Crater Lake in Oregon and Lake Toba in Indonesia. These lakes are often popular destinations for hiking, fishing, and sightseeing.