The Gashnya () is a 20 km long river in southern Bulgaria, flowing through Pazardzhik and Smolyan Provinces. It is a left tributary of the Vacha, itself a right tributary of the Maritsa. There are no settlements along its course.
The river springs at an altitude of 2,018 m from the southeastern slopes of the summit of Batashki Snezhnik (2,082 m) in the Batak Mountain of the western Rhodope Mountains. It flows in easternâÂÂsoutheastern direction in a deep forested valley. At an altitude of 689 m the Gashnya flows into the Tsankov Kamak Reservoir, just upstream of its dam, constructed on the river Vacha.
Its drainage basin covers a territory of 54 km<sup>2</sup>, or 3.3% of the Vacha's total. The Gashnya has predominantly rainâÂÂsnow feed with high water in AprilâÂÂMay and low water in October. Part of the waters along its upper course are diverted west to be utilized for electricity generation at the Batak Hydropower Cascade (254 MW), while the rest are utilized at the DospatâÂÂVacha Hydropower Cascade (500.2 MW).