A dip in Lake Champlain is typically a refreshing and safe activity. However, public beaches are occassionally closed because of waterborne pathogens, which are disease-causing agents such as bacteria, viruses and parasites. Water-related pathogens include E. coli, giardia, cryptosporidiosis, and swimmer's itch (see below). Another recent concern is blue-green algae, which has caused beach closures on Missisquoi Bay.

Water-related pathogens are present in human and animal waste and enter the Lake through point and nonpoint sources. Surface runoff after rainstorms, failed septic systems, storm drains, agricultural fields, and combined sewer overflows are all potential sources of pathogens. These sources are often facilitated by rainfall. For this reason, swimmers should use caution following heavy rain and stay informed about local conditions, especially in the summer.

The Field Guide to Aquatic Phenomena by the Maine DEP and the U. of Maine is a public-friendly guide to understanding what causes different things we see on lakes, such as foam, algae and water quality changes.

Public beaches are sampled for elevated levels of fecal coliform and/or E. coli. (Fecal coliform and E. coli are two different measures of the presence of bacteria from fecal sources. Fecal coliform is the name for the large group of bacteria from fecal sources whereas E. coli is an indicator whose presence is strongly correlated with the presence of pathogens.) When high levels are found, preventing the transmission of disease to humans usually means closing beaches. Unfortunately water testing is often difficult for private beach owners and for popular swimming areas that are not monitored by health departments. Swimmers should use caution at these areas after heavy rainfall, which can wash pathogens into the water.

In Vermont, the health protective level of E. coli bacteria in recreational water is set at 77 organisms per 100 ml of swimming water. In drinking water, however, any fecal coliform presence is a warning sign that action should be taken. In New York, the Department of Health has set a standard for fecal coliform. The fecal coliform density from a series of five or more samples in any 30-day period shall not exceed a logarithimic mean of 200 colonies per 100 ml. When any sample exceeds 1,000 colonies per 100 ml, consideration will be given to closing the beach. See the sidebar in yellow above for beach-specific information.

• Lake Champlain Beaches Map & Article (LC Basin Atlas)

Pollution from E. coli (Escherichia coli) bacteria is a common cause of occassional beach closings along Lake Champlain. E. coli comes from animal waste, including that of humans, pets, livestock, birds, and wildlife. In urban areas dog droppings are one of the leading causes of E. coli pollution. Each gram of dog poop has over 20,000,000 E. coli colonies in it. Like other forms of polluted runoff, or nonpoint source pollution, animal wastes are carried into streams and rivers, and eventually Lake Champlain when it rains.

• E. Coli and Beach Closings (Burlington Eco-Info Site)
• Recreational Water Quality in Vermont (VT DOH)
• Scoop the Poop Campaign

Giardia and cryptosporidiosis are gastrointestinal illness caused by parasites. Drinking untreated water and accidentally ingesting water while swimming are common sources. The greatest concern is contamination of private water supplies which do not filter their water. Hikers, paddlers, and other outdoor users should always boil, filter, or chemically treat water from unknown sources.

• Giardia Information - VT Dept. of Health
• Cryptosporidiosis Information - VT Dept. of Health

There are rare and isolated incidents throughout the Lake of swimmer's itch, a skin irritation caused by a free swimming stage of a fluke (a flatworm). The fluke lives part of its life cycle in snails and completes its life cycle in water birds. When water birds are not present, the fluke may mistakenly attempt to burrow into a human's skin, causing itching. There is some public concern that these outbreaks will occur more frequently, although no major outbreaks have been reported recently.

• Swimmer's Itch Fact Sheet - NY Dept. of Health