Skip to main content

Water Pathogens

Pathogens are disease-causing organisms including bacteria, viruses or protozoa that can cause illness.

Minnehaha Creek is an urban stream that receives direct stormwater runoff from streets, which may contain pathogens that can cause illness. To reduce your exposure, we advise people to avoid direct body contact with Minnehaha Creek for 3 days after a rainfall. Body contact can include water in the mouth, eyes, ears or skin. The most common way to get sick is by getting water in the mouth during swimming, but it may be possible to get sick via exposure from canoeing, fishing or wading.

To reduce exposure to pathogens, you should never drink creek water and should wash hands thoroughly with soap and water following contact with creek water. Elderly people, children and people with compromised immune systems are more susceptible to pathogens in surface water than others. Learn more about waterborne illnesses.

Blue-Green Algae

Blue-green algae is "algae" in name only – it is actually a "cyanobacteria" that can produce toxins harmful to people and animals. When water conditions are right, blue-green algae can bloom, covering areas of the water in a thick, dense mat. It is found in lakes, ponds, and slow-moving streams.

Typically blue-green algae can become most severe when there is little wind, abundant sunlight, warm water, and a high amount of nutrients (phosphorus or nitrogen). Excessive nutrients can come from polluted stormwater runoff, runoff from agriculture, fertilizer, lawn waste, or other material that washes into the lake and decomposes. Toxic blooms are more common in the late summer and early fall but can happen at any time during the season.

Blue-green algae blooms typically look like pea soup or green paint. On the other hand, harmless green algae will come in slimy, stringy strands and can look like floating mats. Duckweed is a native plant that can look like algae film but is actually a very small, floating plant. Though not all blue-green algae is toxic, it is best to stay out of the water if you see it. In addition, people and pets should avoid contact with discolored water or areas with visible algae, never drink untreated surface water, and rinse yourself and/or pets off after swimming in any pond, lake or stream.

Blue-green Algae (toxic) and Green Algae (non-toxic)

Contact with blue-green algae blooms can be fatal to pets. In humans it can irritate skin and eyes, make it difficult to breathe, and cause vomiting and diarrhea. Children are at higher risk than adults.

E. coli

A specific strain of the bacterium E. coli (Escherichia coli) produces a toxin that can lead to severe illness. The bacteria can be transmitted by swimming in contaminated water, among other ways. 

According to the Minnesota Department of Health, there are between 160 and 220 of E. coli-related illness are reported in the state each year. Symptoms include abdominal cramps, severe bloody diarrhea, and little to no fever. Learn more about E. coli.

Naegleria fowleri Amoeba

Naegleria fowleri is a rare amoeba that can infect the brain, and most encounters are fatal. According to the Minnesota Department of Health, "Naegleria fowleri is a free-living amoeba commonly found in warm freshwater. It can cause a rare but severe brain infection called primary amebic meningoencephalitis." Infections are often fatal. People can become infected with Naegleria fowleri when contaminated water enters the body through the nose, and it typically occurs when people go swimming or diving in warm freshwater lakes or rivers." Learn more about Naegleria fowleri.

To Report a Suspected Waterborne Illness:

Call the Foodborne and Waterborne Illness Hotline at 1-877-366-3455

For More Information: