GOLF BALLS
I wonder how many guys on here leave their sticks in the trunk of their car during the summer? I am guilty of that, however I do not leave too many spare balls in the trunk. From what I have read it can get mighty hot in the trunk of a car (Mine is not that bad, I have a hatchback so heat escapes from it better than a trunk) Golf Balls are effected by heat, so you really should not leave them sitting in your car's trunk.
Plus, clubs are effected by the heat, the epoxy will actually loosen up and a club head can move. Grips are effected too.
As for pond balls, it all depends on how long they have been under water. Most courses with water have contracts to have balls removed on a regular basis, so those balls are not sitting in the water very long. I bet the average golfer would not notice much difference in feel and length of those balls. A golfer with an index lower than 10 might notice. JMO and I realize no one agrees with this but hey I can live with that!