Can I snorkel with my apple 4 watch

yes. Here is an excerpt from the watch guide

Apple Watch Series 2, Apple Watch Series 3, and Apple Watch Series 4 have a water resistance rating of 50 meters under ISO standard 22810:2010. This means that they may be used for shallow water activities like swimming in a pool or ocean. However, Apple Watch Series 2, Apple Watch Series 3, and Apple Watch Series 4 should not be used for scuba diving, water skiing, or other activities involving high velocity water or submersion below shallow depth.

Important handling information - Apple Support