Why can't you swim in glacier water?

You should not swim in glacier water because it is extremely dangerous and can kill you quickly due to its near-freezing temperature and hidden hazards. Glacier water, whether in a glacial lake, river, or directly in front of a tidewater glacier in Glacier Bay, is typically 32 to 38 degrees Fahrenheit, just above freezing, because it comes directly from melting ice. Swimming in water that cold causes cold shock response within one to three minutes, including gasping, hyperventilation, and loss of muscle control, making it impossible to swim. After three to ten minutes, you lose dexterity and cannot hold onto a boat or life jacket. Hypothermia sets in within 15 to 30 minutes, leading to unconsciousness and drowning, even for strong swimmers. Glacier lakes and rivers also have other dangers. They are often filled with fine rock flour that makes the water cloudy so you cannot see rocks, deep holes, or currents, and they have extremely strong, unpredictable currents from meltwater. Near tidewater glaciers in Alaska, there is danger from calving ice, where house-sized chunks of ice break off and create massive waves that can swamp boats and swimmers. There is also danger from hidden ice under the surface. National Park Service rangers in Glacier Bay and Glacier National Park prohibit swimming near glaciers for these reasons. Even wading can be dangerous due to cold and currents. So while the blue water looks inviting, it is deadly cold.