Drinking Water

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).


Drinking Water Safety

Potable water is only available seasonally (typically end of May-end of September)in Rock Harbor and Windigo. All surface lake and stream water should be considered contaminated with pathogens. Drinking contaminated water can make you very sick. Water collected at the park should be boiled at a rolling boil for at least one minute or passed through at least a 0.4 micron filter (using a water filter).

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. By itself, chemical treatment is not an effective method of water purification. If you boil your water, bring plenty of stove fuel. If filtering, bring a replacement cartridge for filters that cannot be cleaned in the field.

SteriPENs and other UV purifiers have not been manufacturer-tested for a common parasite found on Isle Royale and cannot be considered effective.

If you have further questions regarding safe drinking water, contact the park.

Canoe at water's edge with blue-green algae bloom on lake's surface surrounding it.
An example of a blue-green algae bloom.


Blue-Green Algae

In recent years, blue-green algae blooms have occurred seasonally in several inland lakes. Blue-green algae can be toxic, and filtering does not remove toxins from the water. Avoid swimming, fishing, or filtering water if it has a cloudy-blue cast or looks like "pea soup." Report possible algae blooms to park staff. If algae blooms occur, advisories will be posted at park visitor centers, affected lakes and campgrounds, and in website alerts.

Last updated: January 12, 2018

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Mailing Address:

800 East Lakeshore Drive
Houghton, MI 49931


(906) 482-0984

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