Lake Superior water temperature

This guide is for anyone planning to swim, wade, paddle or just stand on the rocks on the North Shore. It gives NOAA's own numbers, says exactly what each one measures and what period it covers, and then turns to the National Weather Service's cold water safety guidance. That guidance matters more here than on almost any other lake in Minnesota.

Where these numbers come from

Two NOAA sources, measuring two different things:

NOAA describes GLSEA as "a digital map of the Great Lakes surface water temperature, with ice cover during the winter months, that is produced daily." A lakewide average blends the open lake, which stays cold, with shallow bays that warm faster. So the GLSEA figure tells you the season, and a nearshore reading tells you the day. Buoy 45027 is owned and maintained by the University of Minnesota Duluth, and NOAA publishes its data.

Lake Superior water temperature by month

These are NOAA's long-term (1995-2025) lakewide average surface temperatures for the 1st of each month, plus the 15th from June through October, rounded to a tenth of a degree. NOAA's file lists days by day of the year, so the dates below are that day number read as a 2026 calendar date. The 2026 column is the same day this year, from the same NOAA file.

What the table shows:

• The lake warms late. The long-term average does not pass 50°F until about July 11. Lake Superior is still far colder in June than the air temperatures on shore suggest.
• The warmest stretch is mid-August to early September. The long-term peak is 61.3°F on August 15. In 2026, the lakewide average peaked at 63.9°F on September 6.
• Fall water is warmer than June water. On October 1, the long-term average (55.1°F) is far above June 1 (39.3°F).
• As of November 10, 2026, the latest day in NOAA's file, the lakewide average was 47.4°F, against a long-term average of 45.2°F for that date.

How warm does it get in a hot year?

From NOAA's year-by-year file, the highest single-day lakewide average in each year since 1995 ranges from 58.4°F (2014) to 68.5°F (August 18, 2016). The 2010 peak was close behind at 68.4°F. In no year since 1995 has the average surface of the whole lake reached 70°F.

Nearshore water can swing fast

The buoy at McQuade Harbor, just northeast of Duluth, shows how much the water right off the Minnesota shore can swing. NOAA does not publish monthly averages for this buoy. The figures below are monthly averages calculated from NOAA's raw 2025 buoy readings (taken every 10 minutes), along with the lowest and highest single readings each month, converted from Celsius:

On the evening of July 28, 2025 (July 29 in NOAA's UTC timestamps) the buoy read 25.3°C (77.5°F). About two weeks later, on the evening of August 12 (August 13 UTC), it read 5.5°C (41.9°F). The buoy record shows how fast it happens but not why. Water that felt warm one week can be more than 30 degrees colder a couple of weeks later.

The NWS Duluth beach hazards page lists the hazards along the Lake Superior beaches: "rip currents, longshore currents, outlet currents, and channel currents." It publishes a beach forecast for the Lake Superior beaches in the Twin Ports, explains its swim risk levels, and points to weather.gov/greatlakes/beachhazards for other Great Lakes beaches.

Cold water safety on Lake Superior

The National Weather Service's cold water safety page is direct about why Lake Superior's summer numbers are still dangerous:

• "Cold shock can be just as severe and dangerous from water temperatures of 50-60°F (10-15°C) as it is from water at 35°F (2°C)."
• "Gasping for a breath or rapid breathing from sudden immersion can be triggered by water as warm as 77°F (25°C)."
• Cold shock "occurs during the first 2-3 minutes or more" and can cause dramatic changes in breathing, heart rate and blood pressure.
• Physical incapacitation, the loss of muscle control in the arms and legs, "can be felt within seconds of entering cold water."
• Hypothermia begins "when core body temperature drops to 95°F (35°C)."

Put that next to the table above. For most of the year, the lakewide average sits at or below the 50-60°F range the NWS calls as dangerous as near-freezing water. Even the August peak barely clears it.

The NWS advice for anyone on or near cold water:

• "Always wear a life jacket in and around the water."
• "Always dress for water temperature, not for air temperature." That means a wet suit or dry suit for paddlers.
• "Be sure to check the weather and water temperature before you go out on the water."
• Falls "off watercraft, docks, rocks or jetties" are a listed cause of cold water immersion. That applies to the cliff and rock shorelines at places like Shovel Point and Palisade Head.

Before you swim or paddle

• Check the latest lakewide number on NOAA CoastWatch, and remember the shore may differ.
• Check the NWS Duluth beach forecast on the day.
• Expect cold water before mid-July and after early October, and possible cold surges any time.
• Wear a life jacket on any paddle, and dress for the water rather than the air.
• Have a way out of the water that does not require climbing slick rock.
• Swim with someone on shore watching, at a sheltered beach rather than off cliffs.

Related guides: All North Shore guides · Minnesota road trips · Things to do in Two Harbors · Lake Superior agates · North Shore in winter

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Sources

• NOAA GLERL Great Lakes CoastWatch, Average Surface Water Temperature (GLSEA): https://coastwatch.glerl.noaa.gov/statistics/average-surface-water-temperature-glsea/
• NOAA GLERL Great Lakes CoastWatch, Lake Superior long-term average compared to 2026 (CSV, 1995-2025): https://apps.glerl.noaa.gov/coastwatch/webdata/statistic/csv/avgtemps-s_1995-2026_F.csv
• NOAA GLERL Great Lakes CoastWatch, Lake Superior daily average surface water temperature (CSV, 1995-present): https://apps.glerl.noaa.gov/coastwatch/webdata/statistic/csv/all_year_glsea_avg_s_F.csv
• NOAA GLERL Great Lakes CoastWatch, Sea Surface Temperature (SST) products: https://coastwatch.glerl.noaa.gov/satellite-data-products/sea-surface-temperature-sst/
• NOAA National Data Buoy Center, Station 45027, McQuade Harbor Nearshore, MN: https://www.ndbc.noaa.gov/station_page.php?station=45027
• NOAA National Data Buoy Center, Station 45027 standard meteorological data, 2025: https://www.ndbc.noaa.gov/view_text_file.php?filename=45027h2025.txt.gz&dir=data/historical/stdmet/
• National Weather Service, Cold Water Hazards and Safety: https://www.weather.gov/safety/coldwater
• National Weather Service Duluth, Beach Hazards, Know Before You Go: https://www.weather.gov/dlh/beachhazards