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Water temperature in Ontonagon (MI) in September

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Is it warm enough to swim in Ontonagon in September? Average water temperature in Ontonagon in September is 61.3°F and therefore is not suitable for comfortable swimming. The warmest water in Ontonagon in September is 70°F, and the coldest is 49.8°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Ontonagon

Changes water temperature in Ontonagon in September 2025, 2024

To get an accurate forecast for the water temperature in Ontonagon for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Ontonagon, the selected years in the table also show the values of the maximum and minimum temperatures on each of the days of September.

You can choose any other years:

Year 1:   Year 2:


Day 2025 2024 Min Max
September 162.4°F64.9°F59°F69.1°F
September 263.9°F63.7°F58.8°F69.1°F
September 363.3°F63.7°F60.8°F70°F
September 462.8°F64°F61.2°F69.8°F
September 5 64.4°F61.3°F69.6°F
September 6 63.7°F59.9°F69.3°F
September 7 63.7°F59.7°F68°F
September 8 63.1°F59.5°F67.5°F
September 9 63.1°F59.5°F67.1°F
September 10 63.1°F57.6°F67.1°F
September 11 63.5°F54°F66.6°F
September 12 64.8°F52.9°F66°F
September 13 65.5°F52.2°F65.8°F
September 14 65.7°F52.7°F66°F
September 15 66.6°F51.6°F66.6°F
Day 2025 2024 Min Max
September 16 67.1°F49.8°F67.1°F
September 17 67.1°F49.8°F67.1°F
September 18 66.9°F50°F66.9°F
September 19 66.9°F50.5°F66.9°F
September 20 67.1°F50.7°F67.1°F
September 21 66.7°F50.4°F66.7°F
September 22 66.4°F52.3°F66.4°F
September 23 66.2°F53.4°F66.2°F
September 24 65.7°F53.2°F65.7°F
September 25 65.3°F53.2°F65.3°F
September 26 65.5°F53.6°F65.5°F
September 27 65.8°F53.1°F65.8°F
September 28 65.8°F51.4°F65.8°F
September 29 65.8°F51.8°F65.8°F
September 30 65.1°F52°F65.1°F
Ontonagon water temp chart in September

Average water temperature in Ontonagon in September over a decade

20152016201720182019
62.4°F64.8°F60.6°F58.8°F59.4°F
20202021202220232024
59.4°F64.6°F62.2°F59.5°F65.3°F

Ontonagon sea state in September

Chart comparing the height of waves in Ontonagon in September over the past years. The red line indicates the height of the waves when swimming in the sea is prohibited. To view the current sea conditions, click on the graph.

Waves height in Ontonagon in September

Ontonagon water temperature during other months:

You can also view information about water temperature for other months by clicking on the month button below

Where is the warm sea water in September?

Want to know where the water temperature in September is good for swimming? Select the continent of interest, the day of the month and the required water temperature

Region
Date (day and month)
Water temperature: min 60°F
 Average temperature  Maximum temperature

Temperature in neighboring cities

The nearest locations with the average water temperature in September. In addition, the maximum and minimum water temperatures for that month, recorded over the last decade, are shown

AvrMinMax
McLain State Park60.8°F43.3°F70°F
Calumet60.6°F41.5°F69.8°F
Keweenaw Bay61.9°F52.2°F69.3°F
Apostle Islands61°F52.7°F70.2°F
Eagle River59.9°F48.2°F68.7°F
Madeline Island62.2°F54.9°F70.9°F
Big Bay State Park62.2°F54.9°F70.9°F
Washburn62.2°F54.9°F70.9°F
Bayfield62.4°F54.9°F71.1°F
Eagle Harbor59.5°F47.3°F68.4°F

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[1] - The "Blue Flag" is awarded to beaches which fulfill a number of criteria, including: the quality of the bathing water, which must be in accordance with the relevant European Union Directive environmental education and information and beach area management and safety.

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Our report for Ontonagon is compiled using satellite data together with in-situ observations to get the most reliable daily data of sea surface temperatures, surf forecasts, current temperatures and weather forecasts.

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