Harmful bacteria and viruses (pathogens) can be carried to Lake Champlain in water pollution runoff, and in some cases, by direct introduction. Sources include:
- farm runoff (manure)
- wastewater treatment facility overflows
- failing & failed septic systems (human waste)
- pet waste
- human waste dumped from boats
- wildlife (mainly waterfowl) droppings
Harmful bacteria and viruses can cause people to become sick, or in rare cases, die. The state and some towns regularly test the water quality at public beaches around Lake Champlain during the swimming season for bacteria such as E. coli and other fecal coliform (which inlcudes many kinds of bacteria that comes from animal and human waste). When a certain level of bacteria is found, a beach will be closed until those levels drop to a safe level.