Rajjaprabha Dam Reservoir (Chiao Lan)

Cheow Lan Lake — the reservoir behind Ratchaprapha Dam — fills a flooded valley inside Khao Sok National Park with limestone karsts rising straight out of the water on every side. The dam was completed in 1982, and the peaks now scattered across the lake were once hilltops in a forested valley; some of the original tree stumps are still visible below the surface in the dry season. Entry is 300 THB for foreign adults (150 THB for children), charged separately from the Khao Sok headquarters fee, since May 2024 — Thai nationals pay 40 THB for adults and 20 THB for children.

Almost all lake access is by longtail boat from the pier near the dam, roughly 1 to 1.5 hours’ drive from Khao Sok headquarters. Boats run 2,000 THB for two hours or 2,800 THB for three, a flat rate regardless of group size, in vessels carrying 7 to 18 passengers. A day trip is enough to cruise between the karsts and duck into one of the cave systems, some reachable only by kayak, where stalactites hang over shallow pools. Staying overnight on a floating raft house is the better version of the experience — you get the lake at dawn and dusk, when the mist sits low over the water and the day-trip boats haven’t arrived yet.

Insider Tip: Book the raft house, not the day trip, if your schedule allows it. The dam-to-pier transfer and the boat ride out eat up most of a day-trip’s useful hours; an overnight stay turns the same journey into an actual two days on the water instead of one crowded afternoon.

Watch out: The lake’s popularity means peak-season boats (December–February) can feel closer to a shuttle service than a wilderness outing, with multiple boats converging on the same viewpoints and cave entrances. Early departures help — ask your operator for the first available slot.

Bring sun protection, swimwear, and a dry bag for phones and cameras — most of the day happens on open water with no shade. For where to stay before or after the lake, and the rest of the park’s waterfall trails, see the Khao Sok destination guide. Khao Sok National Park itself and Than Sawan Waterfall both make good add-on stops on the way to or from the dam.