Hi Navk,

While there is no way now a river basin can be tagged as a natural basin, deleting the entire relation is not the right thing to do. You could've deleted the natural:water and water:basin tags. Deleting entire relation is loss of valuable information.

It can just be a multi-polygon relation as before.
Refer other examples,
Krishna Basin https://www.openstreetmap.org/relation/11547113#map=5/16.447/76.113

Kaveri Basin https://www.openstreetmap.org/relation/11201998

Kindly refer them and restore the information that you've done away with.