Thi Lor Su Waterfall

Thi Lo Su drops about 250 metres down a broad rock face on the Mae Klong Yai River, fanning out to close to 450 metres at its widest tier. Most guides call it Thailand’s largest waterfall — the figures have never been formally surveyed, but nothing else in the country comes close for sheer width. It sits deep inside Umphang Wildlife Sanctuary in Tak province’s Umphang district, remote enough that most visitors budget two or three days rather than a single afternoon.

Getting there starts with Highway 1090, the “Death Highway” between Mae Sot and Umphang — 164 km and 1,219 curves through mountain jungle along the Myanmar border, a 3-4 hour drive on its own. From Umphang town, access to the waterfall itself depends on the season. From December through April, 4WD pickups cover most of the unpaved 45 km road, leaving a short walk to the falls — the easy, self-drive-friendly window. From June through October the road closes for safety and to let the trail recover; the only way in during those months is an organised rafting trip down the Mae Klong Yai River followed by a jungle trek of two to three hours, booked through an operator in Umphang town. Closure dates shift slightly year to year, so confirm current status before planning around the edges of that window.

The falls step down through several tiers, each with its own pool. The lower pools are the ones people actually swim in — cold, clear, deep enough to submerge fully — while the smaller upper tiers suit wading more than swimming. Spray drifts across the whole basin, and the roar of the main drop carries well before the waterfall comes into view through the tree cover. Thick jungle wraps around the site; expect bird calls, the occasional troop of macaques, and, on the wet-season trekking approach, leeches.

Insider Tip: Visit in November or early December. The road usually reopens right after the rains stop, so you get near-peak water volume from the wet season plus the easier dry-season access — the best of both windows before the December-April high-season crowds build up.

Watch out: The rocks around the main pools are slick with algae and spray, and several drownings and falls have been reported over the years, mostly from people climbing onto the upper ledges for photos. Stick to the marked swimming areas.

Camping near the falls is possible with a permit from the ranger station — apply at least seven days ahead. Most independent travellers base themselves in Umphang town instead, treating the waterfall as a long day trip or overnight camp arranged through a local tour operator; public transport doesn’t reach the sanctuary, and the unpaved sections are a poor idea without a high-clearance 4WD.