Water temperature in Marathon Key (FL) in August
Is it warm enough to swim in Marathon Key in August? Average water temperature in Marathon Key in August is 86.7°F and therefore suitable for comfortable swimming. The warmest sea in Marathon Key in August is 90.7°F, and the coldest is 83.5°F. To find out the sea temperature today and in the coming days, go to Current sea temperature in Marathon Key
Changes water temperature in Marathon Key in August 2025, 2024
To get an accurate forecast for the water temperature in Marathon Key for any chosen month, compare two years within a 10 year range using the chart below. In addition to the sea water temperature in Marathon Key, the selected years in the table also show the values of the maximum and minimum temperatures on each of the days of August.
You can choose any other years:
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| August 1 | 88.5°F | 88°F | 85.3°F | 88.5°F |
| August 2 | 88.5°F | 88°F | 85.3°F | 88.5°F |
| August 3 | 89.2°F | 87.6°F | 84.9°F | 89.2°F |
| August 4 | 88.5°F | 87.3°F | 85.5°F | 88.5°F |
| August 5 | 89.6°F | 86.7°F | 85.6°F | 89.6°F |
| August 6 | 89.1°F | 86.7°F | 85.8°F | 89.1°F |
| August 7 | 88.7°F | 86.7°F | 85.5°F | 89.4°F |
| August 8 | 88.5°F | 86.7°F | 85.5°F | 89.2°F |
| August 9 | 88.3°F | 86.5°F | 85.6°F | 89.8°F |
| August 10 | 88°F | 88.2°F | 85.3°F | 89.4°F |
| August 11 | 87.3°F | 88°F | 85.3°F | 90.7°F |
| August 12 | 87.6°F | 87.3°F | 85.3°F | 90°F |
| August 13 | 87.4°F | 88.5°F | 85.3°F | 90°F |
| August 14 | 87.1°F | 88.2°F | 85.3°F | 89.4°F |
| August 15 | 88.2°F | 88.3°F | 85.5°F | 89.4°F |
| Day | 2025 | 2024 | Min | Max |
|---|---|---|---|---|
| August 16 | 88.2°F | 88°F | 85.8°F | 89.1°F |
| August 17 | 88.9°F | 88.7°F | 85.5°F | 89.1°F |
| August 18 | 88.3°F | 87.8°F | 85.5°F | 89.2°F |
| August 19 | 89.1°F | 87.8°F | 85.5°F | 89.1°F |
| August 20 | 88.5°F | 88.2°F | 85.5°F | 88.5°F |
| August 21 | 89.1°F | 87.8°F | 84.9°F | 89.1°F |
| August 22 | 89.2°F | 88°F | 84.7°F | 89.2°F |
| August 23 | 89.1°F | 88°F | 85.1°F | 89.1°F |
| August 24 | 88.9°F | 87.3°F | 85.3°F | 88.9°F |
| August 25 | 88.9°F | 87.1°F | 85.5°F | 88.9°F |
| August 26 | 89.8°F | 87.1°F | 84.4°F | 89.8°F |
| August 27 | 89.6°F | 86.7°F | 84.2°F | 89.6°F |
| August 28 | 89.1°F | 86.5°F | 83.5°F | 89.1°F |
| August 29 | 88.7°F | 86.4°F | 83.8°F | 88.7°F |
| August 30 | 88.7°F | 86.2°F | 84°F | 88.7°F |
| August 31 | 89.1°F | 86°F | 83.7°F | 89.1°F |
Average water temperature in Marathon Key in August over a decade
| 2016 | 2017 | 2018 | 2019 | 2020 |
| 86.2°F | 86.7°F | 86.2°F | 87.4°F | 86.9°F |
| 2021 | 2022 | 2023 | 2024 | 2025 |
| 86.7°F | 86.7°F | 88.5°F | 87.4°F | 88.9°F |
Marathon Key sea state in August
Chart comparing the height of waves in Marathon Key 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.
Marathon Key water temperature during other months:
You can also view information about water temperature for other months by clicking on the month button below
