Asan Barrage is located near the meeting point of two rivers, namely Asan and Yamuna. The barrage has an artificial wetland spread over an area of 4 sq km, which is fed by the Asan River. When the water level goes down, some muddy islands can also be seen in the wetland.
The birds seen here are listed as endangered species by IUCN Red Data Book (International Union for the Conservation of Nature). Visitors can see birds like mallards, red crested pochards, ruddy shelducks, coots, cormorants, egrets, wagtails, pond herons, pallas fishing eagles, marsh harriers, greater spotted eagles, osprey, and steppe eagles in the site.
During the winter season various trans-Himalayan migratory birds take rest here on their way to South India. In the end of October, travellers can see migratory birds from the Pale arctic region. The period from the month of October to November and February to March is the best time to observe birds here. This site is a nesting place of Pallas Fishing Eagle for last 30 years. The site offers a rare opportunity to observe 90% of total waterbirds including 11 species of migratory bird during the winter season. Some of them are brahminy ducks, pintails, gadwalls, common pochards, wigeons, common teals, tufted ducks, and shovellers. The period from the month of May to September is also considered as an ideal season to see birds like painted storks, open billed storks, and night herons here.