Phytoplankton are microscopic organisms that live floating in the water and act as the main producers in the food chain system including in mangrove ecosytems. This study aims to determine the quality of water based on the abundance of phytoplankton in the mangrove ecosystem of Sungai Piring Village, Batang Tuaka District, Indragiri Hilir Regency, Riau Province. This research was conducted in F…