What is a waterproof spotting scope?

Waterproof spotting scopes are designed to totally exclude water from the optical tube. They may be nitrogen purged: filled with dry, inert gas (nitrogen) as an additional barrier to the buildup of internal moisture to prevent internal fogging. There may be seals and optical windows in place as well.  The additional feature of rubber armoring is the final level of ruggedness that helps protects spotting scopes from abrasion, damage, or loss of collimation if it’s accidentally dropped. However, waterproofing isn't meant for submerging. If the spotting scope is submerged underwater for longer than a few seconds, water may begin to seep into the spotting scope causing damage.