Water temperature in Thunder Bay (ON) in August

Is it warm enough to swim in Thunder Bay in August? Average water temperature in Thunder Bay in August is 16.8°C and therefore is not suitable for comfortable swimming. The warmest water in Thunder Bay in August is 21.3°C, and the coldest is 12.1°C. To find out the sea temperature today and in the coming days, go to Current sea temperature in Thunder Bay

Changes water temperature in Thunder Bay in August 2025, 2024

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

Sea temperature

Tides

Weather forecast

You can choose any other years:

Day	2025	2024	Min	Max
1 August	17.7°C	20.7°C	13.8°C	20.7°C
2 August	17.8°C	19.5°C	14.4°C	20.4°C
3 August	17.9°C	19.8°C	14.7°C	21.3°C
4 August	16.6°C	19.7°C	15°C	20.1°C
5 August	17.4°C	19.1°C	13.7°C	19.6°C
6 August	17.7°C	18.8°C	13.2°C	19.6°C
7 August	19.2°C	19.5°C	13.5°C	19.8°C
8 August	18.9°C	19.4°C	13.8°C	19.6°C
9 August	20°C	18.2°C	14.3°C	20°C
10 August	19°C	18.5°C	13°C	19°C
11 August	18.2°C	18.3°C	13.3°C	18.3°C
12 August	17.8°C	17.9°C	13.8°C	18.4°C
13 August	17.3°C	17.9°C	13.3°C	18.8°C
14 August	17.2°C	17.7°C	13.4°C	18.7°C
15 August	17.2°C	18.2°C	14.2°C	18.7°C

Day	2025	2024	Min	Max
16 August	17.1°C	18°C	14.8°C	18.7°C
17 August	16.8°C	18.7°C	14.9°C	19°C
18 August	16.2°C	18.5°C	14.9°C	18.9°C
19 August	16.2°C	18.2°C	15.1°C	18.8°C
20 August	16.1°C	18.2°C	15.2°C	18.6°C
21 August	18°C	18.1°C	14.7°C	18.1°C
22 August	17.5°C	18.6°C	14.2°C	18.6°C
23 August	17.5°C	18.3°C	14.6°C	18.3°C
24 August	17.4°C	18.3°C	13.4°C	18.3°C
25 August	16.5°C	19°C	13.1°C	19°C
26 August	15.9°C	20.2°C	13.6°C	20.2°C
27 August	16.1°C	19.8°C	13.4°C	19.8°C
28 August	16.1°C	19.1°C	13.7°C	19.1°C
29 August	15.9°C	18.4°C	12.9°C	18.7°C
30 August	15.6°C	18.5°C	12.2°C	18.5°C
31 August	15.9°C	18.6°C	12.1°C	18.6°C

Average water temperature in Thunder Bay in August over a decade

2016	2017	2018	2019	2020
18.8°C	16.8°C	15.9°C	14.9°C	17°C

2021	2022	2023	2024	2025
17.6°C	15.6°C	16.5°C	18.8°C	18.1°C

Thunder Bay sea state in August

Chart comparing the height of waves in Thunder Bay in August 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.

Thunder Bay water temperature during other months:

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

Temperature in neighboring cities

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

	Avr	Min	Max
Isle Royale	15.7°C	6.3°C	19.5°C
Grand Portage	15.4°C	7.5°C	19.7°C
Grand Marais	15.5°C	7°C	20.3°C
Eagle River	16.4°C	6.1°C	21.3°C
Eagle Harbor	16.1°C	6.2°C	22°C
Calumet	17.9°C	8.9°C	21.9°C
McLain State Park	18°C	9.4°C	21.6°C
Copper Harbor	16.2°C	7.8°C	20.8°C
Lutsen	16.1°C	6.6°C	20.7°C
Tofte	16.3°C	6.7°C	20.7°C

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Our report for Thunder Bay 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.

Region

Date (day and month)

Water temperature: min 16°C

Average temperature Maximum temperature