Does saltwater affect how long you can hold your breath?

Answer 1

In general, no. Salt water is denser than pure water, and therefore more buoyant. So it takes more energy for you to kick yourself down to a particular depth than it would the same depth in fresh water. The extra energy expended burns more oxygen in your blood stream. But if you were to simply hold your breath face down in salt water and fresh water (of the same temperature and elevation), your breath holding times should be very close.