The Lyevaya Lyasnaya (Belarusian: "Левая Лясная") is a river in western Belarus. At its confluence with the Pravaya Lyasnaya near Kamyanyets, the Lyasnaya is formed. The Lyasnaya is a right-bank tributary of the Bug River northwest of Brest. The average discharge at the mouth of 3.6 m3. The average slope of water surface 0.5 ‰.
The Lyevaya Lyasnaya flows through Pruzhany Raion and Kamenets Raion areas of Brest Voblast of Belarus.
The river flows through: Mylnisk, Kamyanyets, Vuglyany.
Tributaries: Leśna Prawa, Wishnia.