Wak Oya of the Colombo district is a sub river of the Kelani river and a entity that belong Kelani river and the entity that start, as a part of Kelani basin. This is one of the main resources for the many reservoir and man made water strongholds and waterfalls. Wak oya not only a nurture the various reservoirs and many waterfalls. Not only that wak oya also faces Gal Bangalawa where it flows freely. With its picturesque beauty and its wonders scenery where in ancient times also used as the elephant bathing ground it was a picture-perfect dwelling for many visitors.