Don't know about Grand Teton NP, but Glacier NP doesn't care. I have swum in four lakes, all in September, when they are warmest. Surface temp is about 60 (or colder), with a 5-degree drop rather fast. Someone has just finished a 10-year effort to immerse himself in all the named lakes in Glacier, and written about his experiences. Bears are often featured. I will try to find a link. glacierexplorer.com/.../
Don't know about Grand Teton NP, but Glacier NP doesn't care. I have swum in four lakes, all in September, when they are warmest. Surface temp is about 60 (or colder), with a 5-degree drop rather fast. Someone has just finished a 10-year effort to immerse himself in all the named lakes in Glacier, and written about his experiences. Bears are often featured. I will try to find a link. glacierexplorer.com/.../
