Even with free access to a flexible, global open water swimming temperature forecast, sometimes it’s useful to have a local, in-person confirmation of the open water swimming temperature where you’re about to be immersed. You need a thermometer.
Zacro Open Water Swimming Thermometer measures the water temperature in Celcius or Fahrenheit
After several unsuccessful experiments (various cooking thermometers, handheld infrared thermometer, etc.), one, inexpensive reliable, and durable option has proven itself the best open water swimming thermometer. The Zacro Digital Aquarium Thermometer (US$7.99 or $9.99 for a two-pack) does exactly what you want it to do:
  • It quickly reads temperature is in Celsius or Fahrenheit (switching easily between them),
  • The device require so little space in a pocket of your backpack or swim buoy that you will forget you have it until the moment it’s needed,
  • It has a sensor tethered by a long enough (64cm/25″) wire to reach a water surface you’d like to measure beyond arm’s length (i.e., below a seawall like the ones where we swim regularly, below the crest of waves, or if you’re otherwise not ready for closer approach to the water),
  • Power consumption from the LR44 battery it seems almost immeasurably small. Inadvertently powering on or leaving power on for extended periods of non-use seems to have little effect on the battery life exceeding a year of repeated use.
  • The operating range exceeds any plausible open water swimming temperature,
  • Readings are shown to a precision of 0.1˚ (˚C or ˚F). This precision isn’t matched by the claimed accuracy of ‘one degree’ (unspecified if this is ˚C or ˚F), but has proven to be accurate enough.
  • Durable through misuse: although product guidance recommends avoiding submerging the body of the unit in the water, the device has tolerated several full immersions, extended wet storage, and exposure to temperature extremes. Without this the first unit tested might have lasted for more than 2 years of use.
Does this prove it’s the best open water swimming thermometer? No. But it’s hard to imagine what improvements are urgently needed: more accurate, cheaper, smaller, longer lasting, rechargeable, integrated into a watch with tracking? Drop a comment if you’ve found a much better open water swimming thermometer.