How to Properly Measure Water Temperatures In The Open Water

How to Properly Measure Water Temperatures In The Open Water

When Ram Barkai, Ryan Stramrood, Kieron Palframan, Toks Viviers, and Andrew Chin completed their trio of swims in the Patagonia Extreme Swim Challenge, one main issue was dealing with the cold and currents in the Strait of Magellan, Beagle Channel and Cape Horn.

But there were different water temperatures taken:

Barkai’s measurements included Magellan (9°C), Beagle (8°C), and Horn (7°C). In contrast, the Chilean Navy measurements include Magellan (3.9°C), Beagle (7°C), and Horn (8°C).

As every extreme swimmer knows (in both very cold and warm water), every 1°C difference can increase the level of risk.

And this is also true on the other (warmer) end of the heat scale. In other words, just as risky is swimming in very cold water, so is swimming in very warm water. In fact, there are more people who have passed away in warm water and victims of hyperthermia than have passed away in cold water and victims of hypothermia in mass participation swims around the world over the past decade.

What caused the difference in the water temperature measurements?

The Navy uses a laser gun to measure the water temperature. (Note: these devices are not approved by the International Ice Swimming Association because a laser has a tendency to measure a few meters below the water surface where the water temperature is lower.) Barkai and the International Ice Swimming Association uses a wireless floating temperature sensor.

There are, of course, other manufacturers that also make reliable, good water thermometers. Most race directors and many people use various forms of measurement to determine the temperature of the water: pool thermometers, boat thermometers, permanent offshore buoy marine thermometers, and infrared thermometers that instantly produces water temperatures readings when pointed at the water from the lead boat at different points in the race. However, these are not always reliable or accurate. A professional thermometer with a reliable accuracy of +/-0.1°C is recommended.

Barkai explains the possible differences, “When I swam [and ice mile] in Ireland with Anne-Marie Ward and Nuala Moore, we took a bucket of ice, filled it up with water and submerged all types of water thermometers we had. From my Suunto watch, a pool thermometer and wireless floating temperature sensor. The difference between thermometers was between 1 to 2°C in water temperatures above 7-8°C and around 1°C in lower temperatures.

In the sea, it is very different. If the usual current is cold, like in Cape Town, the water temperature a few meters below the surface will always be cold. In some places, the difference is around 4°C, even in the middle of the summer. For example, on the Atlantic side, there is the icy Benguela current. However, if the normal current is warmer and the air temperature is very cold as in northern Europe, then the water below the surface will never get very cold.

A swimmer gets cold mainly in his or her chest, neck and core body. The hands and legs freezes, but that does not take the core body temperature down so quickly. So the consistent water temperature at around surface to 20″ below the surface is the critical one. Additionally, when swimming with a boat, the propeller can create eddies and an upwelling of cooler water around the swimmer.”

Some race directors depend on the official water thermometers that are anchored on permanent offshore buoys or that are reported by the lifeguards. The advantages of these methods are that the water temperatures are measured consistently throughout the year with the same equipment. The disadvantages are that these measurement devices may be off.

Personal water temperature devices are useful also. That is, if you use a Garmin, Suunto or Casio watch thermometers, you will become familiar with its range of temperatures in various conditions. But these watches can vary not only from each other, but also from other methods of measurement.

While ice swims are at the extreme end of the open water swimming spectrum, the athletes in this spectrum are usually well-prepared and trained to swim in water under 5°C without wetsuits or neoprene caps. However, most swimmers find water under 15°C uncomfortable at best, and water temperatures above 28°C have directly led to all kinds of problems in open water swimming competitions.

In FINA-sanctioned races, the water temperature should be a minimum of 16°C and can be called off if the water temperature remains over 31°C for 30 minutes in a race. FINA officials follow the procedure that the water temperature is checked 2 hours before the start in the middle of the course at a depth of 40 cm. However, FINA does not stipulate what kind of water thermometer is used or how long the water thermometer is placed under the water. That is up to the FINA Delegate to determine. Even in the pool environment, FINA does not regulate or stipulate how its pool water temperatures (required to be 25-28°C) are measured.

We believe and recommend that the highest-end professional-grade water thermometer is used. It is a wise long-term investment for race directors, especially those who organize races in what can be considered extreme water or air temperatures by the least prepared athletes in their competitions (e.g., below 16°C or above 25°C).

Additionally, it is always in the best interests of a race director and the athletes for the safety personnel to measure the water temperature at several places along the course – not just in the middle of the course. If the water temperature is consistent throughout the course, the athletes should be informed of this fact in the pre-race instructions. Conversely, if there are colder (or warmer) spots throughout the course, the race director should alert the swimmers of these areas and warn them of the possibility of swimming into cold spots. Generally, an experienced local swimmer will be able to identify these cold spots. Any and all water condition and water temperature hints and latest pre-race information that can be given to race participants is a prudent investment of time and effort on the part of the race organization.

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