If you plan to swim in a natural body of water like a river, lake, pond, or the ocean, it is important to keep in mind the potential health effects of swallowing the water. Awareness of what else might be floating in the water with you is the first step in knowing how to protect your health. Please do not assume that water from lakes, streams, rivers, or springs is safe to drink. Water in a stream, river, or lake may look clean, but it can still be filled with bacteria, viruses, and parasites that can result in recreational water-related illnesses. If you swallow the water while you are swimming, you can get illnesses like giardiasis (caused by the tiny parasite Giardia) or cryptosporidiosis (caused by the microscopic parasite Cryptosporidium).