Umananda Island (from Assamese Uma, another name for the Hindu goddess Parvati, the wife of Shiva; and ananda, “happiness”) is the smallest river island in the midst of river Brahmaputra flowing through the city of Guwahati in Assam, a state in northeast India. The British named the island Peacock Island for its shape.
According to Hindu mythology, Shiva created the island for his wife Parvati’s happiness and pleasure. Shiva is said to have resided here in the form of Bhayananda. According to a myth in Kalika Purana, Shiva burnt Kamadeva with his third eye on Umananda when he interrupted Shiva’s deep meditation, hence its alternative name Bhasmachal (Assamese: bhasma, “ash”; and achal, “hill”; literally, “hill of ashes”).
The Kalika Purana states that Urvasikunda is situated here and here resides the goddess Urvasi who brings Amrit (nectar) for the enjoyment of Kamakhya and hence the island got the name Urvasi sland. It is believed that, worship here on Amavasya day when it falls on Monday brings the highest bliss. The Siva Chaturdasi is the most colourful festival that is held here annually. Many devotees come to the temple on this occasion for the worship of the deity.
According to history, in the year 1694, the Ahom king Supaatphaa ordered his minister Gargaya Handique Phukan to build a Hindu temple, called Umananda Temple. In 1897, an earthquake damaged the temple heavily, but was later repaired by a local merchant. The temple displays mixture of both Hindu Vaishnavism and Shaivism. There are Assamese craftings of Ganesha, Shiva, Parvati, Vishnu, and other Hindu deities. During the repairing work of the temple some new Vaishnavi scripts were written on the walls. Craftsmen also carved figures out of rock on the island.
Maha Shivaratri is widely celebrated in Umananda. Monday is considered to be the holiest day in the temple and the new moon brings bliss to the pilgrims.
Source
https://en.wikipedia.org/wiki/Umananda_Island
http://www.assaminfo.com/tourist-places/56/umananda-temple-guwahati.htm
http://ignca.nic.in/asp/showbig.asp?projid=asgwt0100001
https://allaboutassam.in/2019/06/umananda-temple/