Thi Lo Su waterfall, Waterfall in Umphang Wildlife Sanctuary, Thailand

Thi Lo Su is a limestone waterfall on the Huai Klotho in Umphang Wildlife Sanctuary, Tak Province. It drops about 250 metres over stepped rock faces and spans roughly 450 to 500 metres, with the water dividing into three groups: the tallest and most tiered on the left, a narrower untiered middle, and a lower, broader right section.

The waterfall lies in the Umphang Wildlife Sanctuary, about 3 km from the sanctuary office, on the Huai Klotho, which flows into the Mae Klong. Its Karen name means "Black Waterfall". The site has apparently never been surveyed, so its height of about 250 m and width of roughly 450–500 m are estimates. The Tourism Authority of Thailand later listed it among the nine highlights of its "12 Months, 7 Stars, 9 Suns" campaign.

The waterfall's name comes from S'gaw Karen: Thee Lor Sue means "Black Waterfall". The Karen are among the ethnic groups of the Umphang forest, and the sanctuary that holds the falls is named after the district they share. The Tourism Authority of Thailand made the falls one of its "nine suns" under the 12 Months, 7 Stars, 9 Suns campaign, promoted for the rainbow seen in its spray.

From the Umphang Wildlife Sanctuary office, a 1.5 km nature trail through bamboo and mixed forest leads to the falls, with interpretive signs along the way. A separate path climbs to a viewpoint on the opposite hilltop, about two hours round trip. The dirt access road suits high-clearance pickups or 4x4 vehicles and may be impassable in the rainy season; private cars park in Umphang.

The Karen name Thi Lo Su means "Black Waterfall", and the S'gaw Karen write it ထံလီၤဆူ. The falls have apparently never been surveyed, so the figures of 250 m high and nearly 450 m wide are estimates. The Tourism Authority of Thailand lists it among its "nine suns" for the rainbow seen in the spray.