DiveKit

Turn your Apple Watch into a diving aid. 
Features current depth, maximal depth, wrist-based heart rate, metric/imperial units, and fresh/salt water operation. Easy to check at a glance with its high-contrast display and with intuitive operation, this app is the perfect companion for all your water activities.

DiveKit integrates with the Health app in order to collect and display heart rate and blood oxygen saturation data collected by your Apple Watch.