How to get the elevation data for water bottoms from DEM data?

Discussion created by wileyhk2001 on Nov 27, 2013
I downloaded the ASTER global DEM from the following website:
And I found out that whenever there is water bodies the DEM data looks bumpy and I think it doesn't reflect the actual elevation for the river/lake bottoms.

How can I get the elevation for the river/lake bottoms. i read that from some website that i should overly a different dataset (TIN?) onto the DEM data? where should I get that?