For how long would a 68 kg person have to swim at a fast crawl to use all the energy available in a typical fast food meal of burger

A 68kg person has to swim approximately 2 hours of fast crawl to burn 1500 calories.

Explanation:

We have to consider how many calories has the fast food meal of a burger. Let´s consider they have in between 500 calories and 1000 calories. If we add some soda and fries, maybe we get 1000 calories more. So we would consider that a complete fast food meal with burger, soda and fries, we would be talking about 1500 to 2000 calories.

We need to also consider a lot of factors related to the person and the way he or she swims. So we are using and average answer for de details we have here.

fluid balance is an aspect of the homeostasis of organisms in which the amount of water in the organism needs to be controlled, via osmoregulation and behavior, such that the concentrations of electrolytes (salts in solution) in the various body fluids are kept within healthy ranges. the core principle of fluid balance is that the amount of water lost from the body must equal the amount of water taken in.