Before diving a lake, be sure to check the local altitude to make sure it doesn't require modifications to your dive tables. As you learned during Chapter 6, standard dive tables only apply up to altitudes of 1000 feet, and dives at higher altitudes require special tables or a compensating dive computer. An altitude diving specialty course covers modifications to your tables, and should be completed before you attempt high altitude dives.

If you normally dive in the ocean, be aware that fresh water is less dense than salt water, so you'll need to remove weight from your weight belt when diving a lake. For most divers, removing an amount of weight equal to 2.5% of their total weight, including all equipment, is a sufficient adjustment.