Snorkeling in Thailand costs cheaper as compared to popular spots in Europe and the Mediterranean. It doesn't require any certification or tanks & other expensive equipment like diving suits or regulators. The general assumption seems to be that if you can swim and breathe, you can snorkel.
On the other hand, professional Scuba diving needs certification. It allows you to breathe underwater, while snorkeling allows you to breathe while you are on the surface with your face down.
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