[custom_adv] Across most of the United States, climate change is expected to affect fresh and marine water resources in ways that will increase people’s exposure to water-related contaminants that cause illness. Water-related illnesses include waterborne diseases caused by pathogens, such as bacteria, viruses, and protozoa. [custom_adv] Water-related illnesses are also caused by toxins produced by certain harmful algae and cyanobacteria (also known as blue-green algae) and by chemicals introduced into the environment by human activities. [custom_adv] Exposure occurs through ingestion, inhalation, or direct contact with contaminated drinking or recreational water and through consumption of fish and shellfish. [custom_adv] Factors related to climate change—including temperature, precipitation and related runoff, hurricanes, and storm surge—affect the growth, survival, spread, and virulence or toxicity of agents (causes) of water-related illness. [custom_adv] Heavy downpours are already on the rise and increases in the frequency and intensity of extreme precipitation events are projected for all U.S. regions. [custom_adv] Projections of temperature, precipitation, extreme events such as flooding and drought, and other climate factors vary by region of the United States, and thus the extent of climate health impacts will also vary by region. [custom_adv] Recreational use of ponds, rivers, lakes, and the ocean remains immensely popular in the U.S. and includes activities such as swimming, surfing, snorkeling, paddling, and diving. [custom_adv] According to the National Survey on Recreation and Environment (NSRE), more than 143 million people in the U.S. (61% of the population over the age 16) use surface waters to engage in non-motorized water sports. [custom_adv] While some pollutants in the water are easily identifiable and avoidable, such as plastic and garbage, unseen microbial threats continue to pose serious risk to recreational water users health.