Have you ever gone to your favorite beach and found that it has been closed due to high bacteria levels? Pathogens (disease-causing viruses and bacteria) originating from human or animal waste can enter the ocean from polluted runoff, as well as accidental releases from sewage treatment facilities, ranches and farms. Runoff from urban areas or discharges from improperly maintained sanitary systems on boats are also sources of harmful viruses and bacteria. Humans aren’t the only ones at risk from bacteria in the ocean. For example, the population of southern sea otters is threatened by a parasitic pathogen, called Toxoplasma gondii, which is hosted by cats and is spread through their feces. Once established, the parasite causes brain damage and often death in marine species.