The small dog belonged to a fruit shake vendor at Nai Thon Beach. Apparently, the dog had a fever and was not feeling well. It ventured close to the water, possibly to cool off. It may have been knocked off its feet by the waves and became distressed.
Nai Thon lifeguard Ohm Chnachaitaruearaksa saw the dog in distress and rescued it. Nai Thon lifeguards attempted canine CPR but the dog did not respond.
Source: https://thethaiger.com/news/phuket/dog-drowns-off-nai-thon-beach