is tonle sap a man made or natural lake?

Answer 1

The Tonlé Sap is natural, as a result of the collision of tectonic plates over hundreds of millions of years of the geological evolution of the Earth.

"The lake occupies a depression created due to the geological stress induced by the collision of the Indian subcontinent with Asia."

http://en.wikipedia.org/wiki/Tonle_Sap

Answer 2

Natural, and you can even go by boat up the river from Thailand to Phnom Penh and onto Tonle Sap on the way to Siem Reap