The Trefoil, Glacial lake in Rila Mountains, Bulgaria

The Trefoil is the fifth of the Seven Rila Lakes, lying at 2216 m at the foot of the eastern slope of Suhiya Rid. It has an irregular shape and low shores, measuring 240 m long and up to 200 m wide, with an area of 26 decares and a depth of 6.5 m. It receives water from the upper lakes via Bliznaka and drains through two outlets: a northeastern one crossed by the hiking trail, and a northwestern one on the opposite shore, regarded as the source of the Dzherman River.

The lake basin was carved out millions of years ago by melting glaciers that dug deep depressions into the rock. These masses of ice persisted over long periods and left behind the landform we see today.

The lake's older names, Sredniya Ghol and the Turkish Ortaghol, both mean "middle pool", marking its place as the fifth of the Seven Rila Lakes. The hiking trail passes its northeastern outflow, and the northwestern outflow on the opposite bank is regarded as the source of the Dzherman River.

The lake is reached via hiking trails from a nearby mountain lift, though the route presents demanding conditions. Visitors should bring sturdy footwear, warm layers, and mountain gear, as weather at this elevation can change rapidly.

The water remains frozen between October and June, with ice thickness reaching up to two meters during harsh winters. This long freeze period shapes how the place looks and is accessible throughout the year.