Freshwater Safety


Preventing Waterborne Illnesses

Waterborne diseases are usually spread through contaminated water, and most diseases cause intestinal distress, such as diarrhea and vomiting, and some cases can result in death. Some waterborne illnesses that have been detected in Gallatin County include:


Harmful Algae: Algal Blooms

With the advent of summer comes the time for more active recreating in and around Montana’s abundunt fresh water resources.


Harmful algae blooms can occur in any standing body of water that is exposed to the sun. Some years, under certain conditions, the algal blooms may produce toxins which pose a health threat to animals and people.

The algae responsible for algal blooms occur naturally and during spells of warm weather can multiply sufficiently to color the lake water so that it appears green, blue-green or greenish-brown.  During calm weather, the algae can rise to the surface to form a scum which may look like blue-green paint, or jelly, and may form flocs or mats on the lake surface.

The Gallatin City-County Health Department recommends that the public avoid swimming in waters containing a green, floating scum of algae.  We also recommend that you do not allow domestic animals (livestock and pets) to drink water containing this green algal scum.

In Gallatin County, harmful algal blooms have occurred in the past at Hebgen Lake.   Deaths of domestic animals have been attributed to ingestion of water during those harmful algal blooms.  Hebgan Lake is routinely monitored to detect the presence of any harmful algal blooms.

For more information, see the Montana Department of Environmental Quality’s Toxic Algae Fact Sheet



An infection in the intestines caused by a parasite, it can be contracted by drinking out of streams or water systems that are not treated. It is often found in tap water in undeveloped countries.

Symptoms generally appear within one to three weeks after becoming infected and can include:

      • Diarrhea
      • Gas
      • Greasy stool that can float
      • Stomach cramps
      • Nausea
      • Dehydration

Treatment:  If you think you may have Giardia, contact your healthcare provider for testing and treatment.

Prevention:  The CDC recommends the following prevention techniques:

      • Avoid water (drinking and recreational) that may be contaminated.
      • Do not swallow water while swimming in pools, hot tubs, fountains, lakes, rivers, springs, ponds, streams, or the ocean.
      • Do not drink untreated water from lakes, rivers, springs, ponds, streams, or shallow wells.
      • Do not drink water or ice made from water during community outbreaks caused by contaminated drinking water.
      • Do not use or drink poorly treated water or use ice when traveling in countries where the water supply might be unsafe.
      • If the safety of drinking water is in doubt, do one of the following:
          1. Drink bottled water.
          2. Disinfect tap water by heating it to a rolling boil and letting it boil for 1 minute.
          3. Use a filter that has been tested and rated by National Safety Foundation (NSF) Standard 53 or NSF Standard 58 for cyst and oocyst reduction; filtered tap water will need additional treatment to kill or weaken bacteria and viruses.


CDC Giardia Information

Giardia in Montana


E. coli (Escherichia coli)

E. coli is bacteria in the intestines of humans and animals. Although some E. coli bacteria are harmless, other can cause diarrhea, urinary tract infections, respiratory illness, pneumonia, and other illnesses. E. coli is spread through consumption of tiny amounts of human or animal feces, typically ingested through:

      • Unpasteurized (raw) milk
      • Contaminated water
      • Unpasteurized apple cider
      • Soft cheeses made from raw milk
      • Undercooked meats
      • Contact with cattle
      • Contact with the feces of infected people

Symptoms typically occur three to four days after exposure, and may include:

      • Severe stomach cramps
      • Diarrhea (often bloody)
      • Vomiting

Treatment:  Most people recover without treatment within five to seven days. The consumption of extra fluids is encouraged to prevent dehydration.

Prevention:  The CDC recommends the following prevention techniques:

      • Avoiding swallowing water when swimming or playing in lakes, ponds, streams, swimming pools, and backyard “kiddie” pools.


About E. coli (Escherichia coli)


Swimmer’s Itch

Swimmer’s itch, also called cercarial dermatitis, appears as a skin rash caused by an allergic reaction to certain microscopic parasites that infect some birds and mammals. These parasites are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans). While the parasite’s preferred host is the specific bird or mammal, if the parasite comes into contact with a swimmer, it burrows into the skin causing an allergic reaction and rash. Swimmer’s itch is found throughout the world and is more frequent during summer months.


      • Tingling, burning, or itching of the skin
      • Small reddish pimples
      • Small blisters

Treatment:  Most cases of swimmer’s itch do not require medical attention. If you have a rash, you may try the following for relief:

      • Use corticosteroid cream
      • Apply cool compresses to the affected areas
      • Bathe in Epsom salts or baking soda
      • Soak in colloidal oatmeal baths
      • Apply baking soda paste to the rash (made by stirring water into baking soda until it reaches a paste-like consistency)
      • Use an anti-itch lotion


About Swimmer’s Itch


Cryptosporidium (“Crypto”)

Cryptosporidium is one of the leading causes of waterborne disease, or disease caused by contaminated drinking water or recreational water. Recreational water is water from swimming pools, hot tubs, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with sewage or feces from humans or animals. Below are answers to the most common questions regarding Cryptosporidium and healthy swimming. –From the CDC website.


About Cryptosporidium (“Crypto”)


hyalite reservoir

If you have any questions please contact us at:

Environmental Health Services

215 West Mendenhall, Rm 108, Bozeman

(406) 582-3120