Yes, cold water immersion can be harmful. Risks include hypothermia, arrhythmias, heart attacks, and drowning due to initial cold shock and gasp reflex followed by hyperventilation. Cold water can also lead to exhaustion, making swimming difficult. Experts recommend consulting a doctor before attempting cold plunges, avoiding head-first dives, and planning an exit strategy before entering the cold water. The cold shock response peaks between 50 and 59 degrees Fahrenheit (10 to 15 degrees Celsius), and water colder than this offers no extra benefits.