On Lake Champlain one of the 911 callers who saw the two kayaks get flipped over and flailing about in the stormy waters, got on a jetski and immediately went out to assist, but was unable to find them. (Vermont Digger newspaper)
Even for a strong swimmer, treading water in calm, warm water for 30-minutes without any flotation is a tiring challenge, and different people have different degree of natural float-ability ..... some people are natural sinkers ..... some are natural floaters.
In just five fast months, it will probably be January 3, 2020, and the lake water will be a lot colder .....
https://www.weather.gov/safety/coldwater ..... some good cold water info hey-ah!