The Asan Barrage, popularly known as Dhalipur lake, was created in the year 1967 as a result of the construction of Asan barrage at the confluence of the river Yamuna & Asan through Dhalipur power house. The major attraction of Asan Barrage is bird watching.

The Asan reservoir attracts 53 species of water birds of which 19 are winter migrants from Eurasia. During winter months 90% of the waterbird population comprises the following 11 migratory species, namely Brahminy Duck, Pintail, Red Crested Pochard, Gadwall, Common Pochard, Mallard, Coot, Wigeon, Common Teal, Tufted Duck, and Shoveller.

The Asan Reservoir is a small man-made wetland of approximately 4 sq km area, located 40 km west of Dehradun, on Dehradun-Paonta Sahib road. The barrage is 287.5 m long, the river bed being 389.4 m above sea level, with minimum and maximum water levels respectively at 402.4 m and 403.3 m asl.

The Asan reservoir exists throughout the year and is fed from the river Asan and the discharge channel of Yamuna through Dhalipur powerhouse. Although, the water level is controlled it often goes down, and swampy islands in the middle become visible, attracting a variety of marsh-loving birds like Egrets, Herons and Lapwings, etc.