Sri Lanka locations

I just watched the film for the third time (showed it to my film students), but the first time since visiting Sri Lanka, where the film was shot. The village scenes are clearly old Colombo, but I'm wondering where they shot the river scenes. It seemed like a built-set, as I saw nothing like it on the island. Can anyone help me with this?

I want to shake every limb in the Garden of Eden
and make every lover the love of my life