Illegal filling of ponds for making house and buildings.

There is a pond in front of my house. The whole area is known by that pond and it also gets included in our address. Recently, the owner of the pond has started filling it with soil and also started construction of house on that pond. The whole area is facing the scarcity of water and it seems it will get worse after the pond gets filled. How can I ensure that this illegal activity gets stopped or is it legal for the owner to fill his own pond? Can I directly write a letter to the DM? Please guide me. The pond belongs to Darbhanga from Bihar.