Drinking Water


Stay Hydrated

Dehydration is a serious concern, especially when hiking inland like along the Greenstoe Ridge Trail. Drink plenty of water and eat salty snacks. Campgrounds are the best places to find water to purify in the backcountry. Carry enough water for your planned mileage. Start hikes early and seek shade when needed.

Filtering water from Lake Superior.
All surface lake and stream water should either be boiled at a rolling boil for at least one minute or passed through at least a 0.4 micron water filter (shown here) and disinfected using chemical treatment.


Potable (Treated) Water

Potable water is only available in Rock Harbor and Windigo.

Water in the Backcountry

All surface lake and stream water should be considered contaminated with pathogens (non-potable). Drinking contaminated water can make you very sick.

Of the park's campgrounds, 35 out of 36 are either located along Lake Superior or an interior lake, making water access easy to obtain.

Treating Your Own Water in the Backcountry

Use one of these methods:

  • Physical Purifier: Use one that is rated to remove viruses.
  • Water Filter (0.4 microns or finer) + Chemical Treatment (use tablets or bleach).
  • Water Filter (0.4 microns or finer) + UV Treatment (use a UV purifier).
  • Boil: At a roiling boil for at least one minute (bring plenty of fuel canisters).

Filtering Water Details

To be assured of no risk of contamination from small bacteria and viruses, all filtered water should be further treated with iodine or other approved chemical methods. If filtering, bring a replacement cartridge for filters that cannot be cleaned in the field.

Chemical Treatment Details

By itself, chemical treatment is not an effective method of water purification.

UV Purifiers Details

SteriPENs and other UV purifiers have not been manufacturer-tested for hydatid tapeworm, a common parasite found in Isle Royale waters and cannot be considered effective. Hydatid tapeworm (Echinococcus granulosus) is a parasitic tapeworm that requires two hosts to complete its life cycle. On Isle Royale, moose host larval tapeworms, which form hydatid cysts in their body cavity. In wolves, larval tapeworms mature and live in the small intestine. Adult tapeworms produce eggs which are expelled from wolves in feces, and consequently, the waters of Isle Royale. Find out more about hydatid tapeworm on the Center for Disease Control's website.

More About Water Purification

For detailed water purifying information, visit the National Park Service Backcountry Health website. If you have further questions regarding safe drinking water, contact the park.


Cyanobacteria and Harmful Algal Blooms

In recent years, harmful algal blooms have been present periodically at several inland lakes. When filtering and/or purifying water, these HABs must be avoided completely as there is currently no viable method for removing or subduing cyanotoxins in the backcountry.
Learn more about harmful algal blooms, how to identify them, and what to do if you find them.

Stay up-to-date on the Current Conditions at Isle Royale National Park, including any current advisories regarding HABs.


Last updated: October 2, 2023

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