Healthy Tahoe: Cold water safety this summer

Kimberly Evans, MD

Summer is here, and after last summer’s lockdown, locals and visitors alike are ready to get out and experience Lake Tahoe. Before hitting the water, consider water surface temperatures and the effects of cold water immersion.

Symptoms of cold water immersion can occur at water temperatures as warm as 77 degrees; Lake Tahoe’s water temperatures average about 50–60 degrees in early summer, warming throughout the season to 65–75 degrees. There are four stages of cold water immersion.

Stage 1: Initial cold shock

Sudden immersion into cold water can cause immediate, involuntary gasping for air, panic and vertigo, as well as create changes in your body’s blood pressure and heart rate. The sensation of taking your breath away can result in panic and inhalation of water and drowning. If you do fall in or enter the cold water, attempt to get control of breathing and try not to panic. Focus on floating with your head above water, until the initial cold shock phase passes. If it doesn’t pass, it’s time to get out of the water.

Stage 2: Short-term swim failure

Swim failure occurs anywhere from three to 30 minutes following the initial cold water shock. In this phase, the muscles and nerves in the legs and arms will begin to cool quickly, causing strength and movement to drop significantly. Even a person in good physical condition may be unable to pull themselves out of the water or keep their head above the water. It’s recommended to not swim alone in Lake Tahoe, and if you or someone you’re with experiences short-term swim failure, place your body in a floating position if possible and get to shore or aboard a watercraft quickly to begin rewarming measures.

Stage 3: Long-term immersion hypothermia

Hypothermia sets in after 30 minutes of cold water exposure, depending on the water temperature, as cold water causes the body to lose heat 25 times faster than cold air. Hypothermia is a cooling of the body’s core temperature caused by active heat loss and the failure of the body to produce more heat.

Signs of hypothermia include: shivering slurred speech, cold and bluish lips, skin and fingernails, loss of feeling in extremities, confusion, dizziness, and rigidity in extremities. If hypothermia is suspected, take action by starting rewarming measures and call 911 or go to the closest medical facility.

Stage 4: Post immersion collapse

Post immersion collapse can occur at any point and your body is still in danger while being rescued from cold water or after. Cardiac arrest after cold water immersion occurs due to the collapse of blood pressure. Along with hypothermia, possible water in the lungs due to inhalation, or coagulation issues due to cold and thickened blood.

To have a fun, safe time on the water, wear a personal flotation device at all times. If you’re operating a boat, ensure there are life jackets for every passenger aboard. Avoid jumping off large rocks into deep water, as this runs the risk of both cold water immersion and trauma.

Recognizing the four stages of cold water immersion and signs of hypothermia prevents emergencies, injuries and helps to keep you and your family safe around the lake this summer.

Dr. Kimberly Evans is a surgeon and the Trauma Program Director at Barton Health. Barton’s Level III Trauma Center provides medical services for trauma care and the immediate availability of emergency medicine physicians, surgeons, nurses, lab and x-ray technicians, and life support equipment 24-hours a day. Learn more at

Two people jumping off Lake Tahoe's famous Bonsai Rock. (Getty Images)


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