Beach Health & Water Quality

Waterborne Pathogens

What are Waterborne Pathogens?

Pathos is Greek for suffering, and -gen is a suffix meaning producer, also from Greek. Thus, a waterborne pathogen is a disease maker that occurs in the water. These “germs” are living microscopic organisms-microorganisms or microbes--that take in food, give off wastes, grow, reproduce, and die. The most common types of waterborne pathogens are bacteria, but they also include viruses, protozoa, and certain kinds of algae. Not all microorganisms, however, are harmful. In fact, most microorganisms are beneficial and we depend on them, for example, as producers of foods (for example, cheese, yogurts, and other dairy products) or as decomposers of wastes and nutrient recyclers.

Pathogen Pathways

Most microorganisms thrive in places that are warm, wet, dark, and rich in nutrients. Our intestinal tract is all of that and therefore an ideal environment for many pathogens to live and multiply. An infected animal or human host daily excretes millions of pathogenic microbes. The majority of these will not survive the harsh conditions of the outside world. But some of them may find their way into lakes and streams and, perhaps, from there into another host. Almost always, waterborne pathogens enter the water with waste. The waste enters the water with runoff from developments or feedlots, direct releases of untreated sewage, or indirect releases from underground leaks of sewage pipes. Other common sources of pathogens in the water or at the beach are the droppings of seagulls and waterfowl or pet wastes.


Bacteria—tiny, single-celled life forms visible only under a microscope—cause most waterborne diseases. But not all bacteria cause harm and disease. Bacteria are in fact the most common life forms on the planet and play many critical roles in the food chain, as decomposers, and by recycling nutrients essential for animals and plants. Key bacterial pathogens responsible for waterborne disease include Salmonella typhi (typhoid fever), Shigella (shigellosis), and Vibrio cholerae (cholera). These pathogens measure from 0.4 to 14 ?m (one ?m or "micrometer" equals one one-thousandth of a millimeter) in length and 0.2 to 1.2 ?m in width.

Fecal Coliform
Fecal coliform

Fecal coliform bacteria are a group of bacteria that occur in large numbers in the gut and feces of humans and other mammals. They enter streams and lakes with sewage or wastes. Most fecal coliforms are normal inhabitants of the digestive tract and considered relatively harmless. In fact, their absence can lead to some types of vitamin deficiencies in humans. However, their detection in water may indicate the presence of more harmful microorganisms found in feces. E. coli is the major species of the fecal coliform group.


Escherichia coli (or E. coli for short) is a common bacterium that lives in human and animal intestines, where it is present in large numbers. There are hundreds of E. coli strains and most are relatively harmless, causing illnesses such as traveler’s diarrhea only when consumed in exceedingly high numbers. A notorious exception is E. coli strain 0157:H7, an emerging pathogen that produces a powerful toxin and can cause severe illness. E. coli O157:H7 was first recognized as a cause of illness during an outbreak in 1982 traced to contaminated hamburgers. Since seen, incidents were also reported were people became sick after drinking or swimming in water contaminated by E. coli 0157:H7. Symptoms of poisoning by E. coli 0157:H7 include bloody diarrhea, kidney damage, and occasionally death.


Aeromonads are bacteria that are found naturally in lakes and streams. In large numbers, they can cause wound infections. Usually, the concentration of aeromonads in the water is too low to pose any health risk. But certain conditions-warm water combined with excess loadings of nutrients-can cause aeromonads to grow and multiply explosively. Such massive growth of aeromonads can put persons with compromised immune systems at risk for wound infections.

Other Pathogens


Viruses are tiny bundles of genetic material-either DNA or RNA-carried in a protein shell that protects them from environmental hazards. Ranging in size from 0.02 to 0.09 ?m, they are much smaller than bacteria and making them visible requires sophisticated electron microscopy techniques. Viruses are inanimate until they come in contact with a suitable host cell. They exist for one purpose only--to reproduce. To do that, they inject their genetic material into a host cell and take over its reproductive machinery. Several viral agents for waterborne diseases have been detected in nearshore waters of the Great Lakes. They include hepatitis A virus, which is the agent causing infectious hepatitis. Norwalk, rotavirus, and some other types found in Great Lakes waters can cause viral gastroenteritis.


While most protozoa (“little animals” in Greek) in the water are part of the natural community in a lake, some are intestinal parasites in animals that can be transmitted to humans and cause disease. In the Great Lakes region, Giardia lamblia and Cryptosporidium are the protozoans that are of most concern as agents of waterborne disease. When discharged by an infected host, these intestinal parasites enter a resting stage and form durable cysts that can survive chlorination and many other disinfection methods. Filtration is the most reliable technique to remove Giardia and Cryptosporidium from the water. Giardia cysts are approximately 8-12 ?m in size, Cryptosporidium cysts 4-6 ?m.

In 1993, an operation failure at a water treatment plant in Milwaukee led to a massive outbreak of cryptosporidiosis. The outbreak was the largest documented water-borne disease outbreak in the United States since record keeping began in 1920. An estimated 403,000 persons became ill, of whom 4,400 were hospitalized. Several deaths of immunocompromised patients were reported as a result of the infection. During the nineties, there were also several smaller outbreaks of cryptosporidiosis in Ontario due to contaminated drinking water. Giardia lamblia gained notoriety some years ago when an outbreak occurred in Banff National Park. This giardiasis outbreak was termed by the media as beaver fever because the local beavers were thought to be the source of contamination of the water supply. Giardia lamblia is a growing concern since the number of reported infections in the Great Lakes region has been increasing in recent years.

Blue Green Algae

Concentrations of nutrients (from fertilizers, manure, septic systems, etc.) in lakes above the natural levels can cause algae to grow and reproduce at high rates in what is called an “algal bloom”. Some species of blue-green algae (or cyanobacteria) can release toxic substances as they bloom. One example is microcystis, a toxic blue-green alga that has recently reappeared in Lake Erie. Exposure to the toxins of microcystis may lead to gastrointestinal distress. Risk is greatest when algal blooms are thickest and for those who are most likely to ingest lake water (i.e. children and pets). Even so, there have never been any reports of individuals in the Great Lakes region becoming ill from exposure to microcystis. However, microcystis blooms in ponds have reportedly caused the death of cows, sheep, and even dogs drinking from the water.