Airswim

Air Swim is an unexplained phonomena that allows mario to reach points on the Y co ordinate that he was previously unable to. The height of an air swim varies and is just pure luck. You cannot travel below the water level. The cause of air swim is mostly unknown but it is thought to be caused by a loading error, similar to the believed cause of the unexplained fog glitch. You cannot get an air swim with any sort of setup, only by chance

Uses

Air swim would be invaluable in Lake Kingdom Koopa Freerunning if someone were to get an air swim of the perfect height. Theoretically, one could get an airswim to the height of the boss arena platform where the goal is situated. In this situation, the player could move from the platform with the fishing pond directly to the goal instead of taking a detour to the Lake Lamode City. Using mods, players have given themselves air swim to see what time could be achieved. So far, the best air swim time is a 14 second time. Whereas the usual world record is only 16 seconds

Sightings

Here is a spreadsheet detailing all known air swim sightings.