Also the Grand Canyon, which attracts much more people than the Boston Marathon:
However, a 6-year study reported that exercise-associated hyponatremia, dehydration, and heat exhaustion occurred at nearly the same rate, prompting re-examination of emergency protocols. Most exercise-associated hyponatremia cases at the Grand Canyon occur among summer hikers to the inner Canyon and are often misdiagnosed as exertional heat illness due to overlapping signs and symptoms.
Hyponatremia is especially dangerous because a common response is to drink even more water, which makes the condition even worse. The National Park Service changed all their hiking advice to explicitly recommend "salty snacks" and "sports drinks".
However, a 6-year study reported that exercise-associated hyponatremia, dehydration, and heat exhaustion occurred at nearly the same rate, prompting re-examination of emergency protocols. Most exercise-associated hyponatremia cases at the Grand Canyon occur among summer hikers to the inner Canyon and are often misdiagnosed as exertional heat illness due to overlapping signs and symptoms.
https://journals.lww.com/cjasn/fulltext/2024/05000/exercise_...
Hyponatremia is especially dangerous because a common response is to drink even more water, which makes the condition even worse. The National Park Service changed all their hiking advice to explicitly recommend "salty snacks" and "sports drinks".