The Emerald Pool and the Blue Lagoon are part of the Khao Phra Bang Khram Nature Reserve, and their waters come from thermal hot springs that are deep underground. As such, the whole area becomes a hotbed for backpackers and tour groups from all over south eastern Thailand, and this leads to a lot of cramped conditions, where your enjoyment of the pools will be curtailed by the sheer number of people sharing the space with you.