A comprehensive recirculation and water quality study has been carried out to investigate the feasibility of extending the plant capacity of Umm Al Nar Power and Desalination Plant. The plant is located within the complex lagoon system around Abu Dhabi Island. The study comprised field measurements and application of hydrodynamic and water quality numerical models. The hydrodynamic situation around the plant showed a characteristic feature due its location inside Abu Dhabi lagoon system far from the sea. A pool extending over a large area around the plant is created with higher temperature and salinity due to the compounding effect of continuous input of additional heat and salt from the plant into the lagoon system. The plant subtracts its cooling water from this pool on the one side and discharge its hot brine to it on the other side. The extent and elevated temperature and salinity levels in the pool depend on flow characteristics in lagoon system and location and additional heat and salt inputs from the plant. The paper describes the field measurements and model simulations and presents their results.