Swimming in a natural body of water, such as a lake, pond, or reservoir, carries a risk of becoming ill because these environments are not chemically treated like swimming pools. Lakes contain a complex ecosystem where various microorganisms and contaminants can thrive, potentially causing recreational water illnesses. Understanding these risks and implementing preventive actions is the most effective way to safely enjoy natural waterways.
Common Waterborne Illnesses and Symptoms
Gastrointestinal sickness is the most frequent type of illness contracted from lake water, primarily caused by accidentally swallowing water contaminated with fecal matter. Parasites like Cryptosporidium (Crypto) and Giardia are problematic because their protective outer shells allow them to survive in the environment for extended periods. Symptoms of these infections, which include watery diarrhea, stomach cramps, nausea, and sometimes a low-grade fever, can appear anywhere from a few days to two weeks after exposure.
Bacteria like pathogenic E. coli and Shigella also cause gastrointestinal distress, often resulting in bloody diarrhea and abdominal pain. Beyond the digestive system, other microorganisms can cause skin, eye, and ear infections. Folliculitis, often caused by the bacterium Pseudomonas, manifests as an itchy, bumpy rash or pus-filled blisters, frequently appearing on skin covered by a swimsuit.
Another common skin reaction is Swimmer’s Itch (Cercarial Dermatitis), an allergic response to microscopic parasites released by infected snails. These parasites burrow into the skin, causing tingling and an itchy, pimple-like rash that typically resolves on its own. Water trapped in the ear canal after swimming can lead to Otitis Externa, commonly known as Swimmer’s Ear, an infection caused by bacteria thriving in the moist, warm environment. More serious, though rare, bacterial infections like Leptospirosis can be contracted if contaminated water enters the body through an open cut, leading to flu-like symptoms and potentially severe complications such as kidney or liver damage.
Environmental Factors Affecting Water Safety
The concentration of pathogens in lake water is heavily influenced by external sources of pollution and natural environmental conditions. Runoff from surrounding land is a major contributor, carrying contaminants like animal waste, fertilizers, and sediment directly into the water, particularly after heavy rainfall. This non-point source pollution often includes bacteria and parasites from agricultural operations, stormwater overflow, and failing septic systems.
Nutrient pollution, specifically high levels of nitrogen and phosphorus from fertilizers and sewage, fuels the rapid growth of cyanobacteria, commonly known as blue-green algae. These dense growths are called Harmful Algal Blooms (HABs), and they produce cyanotoxins that pose a direct health risk. Exposure to these toxins can cause skin irritation, respiratory issues, and gastrointestinal symptoms.
Water temperature and depth also play a significant role in microbial safety. Warmer water, increasingly common during summer months, encourages the faster growth and proliferation of most bacteria and algae. These warmer conditions can also favor the growth of specific pathogens, such as Vibrio bacteria, and extend the duration of HABs. Low water levels can also concentrate existing pathogens and toxins, thereby increasing the risk of exposure for swimmers.
Essential Safety Measures Before and After Swimming
Reducing the risk of contracting an illness begins with checking the water conditions before entering the lake. Swimmers should look for local health department advisories or posted signs indicating closures or warnings about bacteria levels or harmful algal blooms. A simple visual inspection is also helpful; avoid water that appears cloudy, discolored, has a foul odor, or visible scum, foam, or algae mats. It is advisable to avoid swimming for at least 48 hours following a heavy rain event, as runoff is most likely to have washed high concentrations of pathogens into the water during this time.
While swimming, preventing the ingestion of lake water is the most effective safety measure against gastrointestinal illness. Swimmers should keep their heads above water and refrain from swallowing the water. If there are any open cuts, scrapes, or wounds, they should be fully covered with a waterproof bandage to prevent bacteria like Pseudomonas or Leptospira from entering the bloodstream.
Immediately after leaving the water, thorough hygiene is necessary to remove potential contaminants from the skin and hair. A full shower with soap and clean water should be taken as soon as possible, as this washes away lingering bacteria, parasites, or toxins that could cause rashes or infections. To prevent Swimmer’s Ear, it is important to dry the ears completely after showering, tilting the head to encourage trapped water to drain. If symptoms such as persistent, severe diarrhea, high fever, or signs of dehydration develop, medical attention should be sought promptly.