Open Water Swimming Related Health Issues
The biggest challenge that a swimmer will have at the Horsetooth Swim is handling the colder water for the extended period. Being a high altitude lake, the water temperature stays relatively cool year round. At the time of the swim, it typically warms up to 65-70F. To complicate things, we abide by international rules for long distance swims where wetsuits are not allowed. Only one division of the 2.4 mile swim is a wet suite swim.
In our experience, the cold water is the biggest challenge endurance athletes have to overcome. We are not sure how you will get acclimated to the cold water but we will warn you to take the temperature seriously. In 2002, despite the much publicized drought we were experiencing, the water temperature dropped to 62F for the swim. None of the locals had been training in cold lakes since all the lakes were warmer then normal due to the drought. The colder temperature in Horsetooth still remains a mystery to us even though we have some theories. Anyway, the result was a record number of DNFs due to the cold temperature. The medics had to treat two cases of hypothermia. Unfortunately, we do not have control of the water temperature.
Even in 2008 with the water temperature in the 70s, we had swimmers that did not finish the race due to hypothermia.
Some information on hypothermia is available at hypothermia.org.
Swimming Induced Pulmonary Edema
Swimming Induced Pulmonary Edema (SIPE) is a fairly rare condition. It is similar to High Altitude Pulmonary Edema (HAPE) that is well known to moutaineers. In both cases, fluid fills up the lungs. In these cases, the fluid is not from an external source, but rather from the blood vessels themselves. If enough fluid collects in the left lung, it will start to prevent the heart from beating as normal. This is a medical emergency. If this happens, the swimmer should stop as soon as possible and get Dive Rescue and/or the EMTs to them as soon as possible. The "good" news is it's pretty easy to detect. A swimmer will mostly likely be coughing and spitting up a pink frothy sputum as well as complaining of shortness of breath, note that chest pain is not a symptom. Articles on swimming induced pumonary edema include: The Journal Chest.