This question is an exact duplicate of:
I am using SAR image and SNAP tool to extract water bodies. Followed the below link ( http://www.un-spider.org/advisory-support/recommended-practices/recommended-practice-flood-mapping/step-by-step) and could extract the water bodies successfully.
However, the problem what I am facing is along with the water bodies, standing water with crop fields are also extracted.
How can that be avoided?