The magnificent underwater world of Ko Mak is as great a place to dive as anywhere else. Especially a little west of Ko Mak at the Mu Ko Rang, which falls under the jurisdiction of the Mu Ko Chang National Park. It is considered the best site in Trat for both snorkelling and scuba diving.

Mu Ko Rang comprises different sized islands; such as, Ko Rang, Ko Kra, Ko Tian, Ko Yak, Ko Sam Phi Nong and Ko Ma Pring; just to name a few. The most popular diving sites focus around Ko Rang and Ko Kra. On most days, with a sunny and open sky, the water will be crystal clear, revealing abundant and gorgeous coral reefs. Onlookers could be treated to schools of a variety of fish, like barracudas, lionfish, blacktip groupers, leopard groupers, yellowtails and more. They turn the ocean waters into a moving canvas of colour.

There are the twin islands like Ko Rayang Nai and Ko Rayang Nok, located 1km southwest of Ko Mak, which is just a 5-minute boat ride. Ko Rayang Nai is closer to Ko Makžs Laem Tukkata. The island has a mountainous terrain and an abundance of trees, but no beaches. It offers both diving and kayaking.

Ko Rayang Nok, on the other hand, has a long white sandy beach that is great for swimming and snorkelling. Just a few steps from the beach and the water becomes brilliantly clear. Beneath the surface is the coral and another diverse array of fish; such as, Indian mackerels and parrotfish. The island is home to the Rayang Phurin Resort, which always welcomes tourists.

There are also other beautiful diving sites near Ko Mak, like Ko Kham and Ko Phi.

For diving enthusiasts, there are many diving shops on Ko Mak that offer lessons and package tours at the different diving sites around the island.