Despite the significant efforts to reduce nitrogen discharge from wastewater treatment facilities (WWTFs), the Long Island Sound (LIS) area affected by hypoxia actually increased over the last decade. Our preliminary research has suggested that WWTFs utilizing the biological nitrogen removal (BNR) process may actually increase particular forms of N that are more potent for algal bloom in LIS. We propose a research plan to evaluate the true impact of upgrading WWTF for N removal (i.e., BNR) on receiving water eutrophication and toxic algal bloom.