I recently got an Apple Watch Series 2 and I know it has water resistance up to 50 meters. I sometimes take it to the pool and it works fine there. In a few days I am going for a swim in the ocean and am going to swim there for a while. I just want to ask if the Apple Watch Series 2 is capable of being in seawater, which has salts rather than regular pool water.
It depends on what you do with it:
Apple Watch Series 2 may be used for shallow water activities like swimming in a pool or ocean. However, Apple Watch Series 2 shouldn't be used for scuba diving, water skiing, or other activities involving high velocity water.
From Apple Support.