This study has been intended towards detecting the spatial and temporal variation of the dissolved organic substances in three major river systems of Sundarban mangrove forest. The Sundarban is important for Bangladesh both from the economic and ecological point of view. So, the policy makers should come forward with urgent strategies to protect this forest from the impending danger of severe aquatic pollution. This book will chronologically explain different water quality parameters in two seasons which might be used as a guideline for further study.