ConclusionsThe relation between eutrophication (and consequently algaeavailability) and the production of bioethanol are described in thispaper. Two case studies are analysed: the Orbetello Lagoon andKøge Bay, located in Italy and Denmark, respectively. In these twosystems, the flow of nutrients into the shallow waters leads toan undesired flowering of macroalgae. The death and decompo-sition of macroalgae decreases oxygen in the water, preventingrespiration of other organisms. In the Orbetello Lagoon, macroal-gae are harvested directly on the water to avoid anoxia events,while in Køge Bay, waves and tides carry the macroalgae to theshore, where special machinery collects them in order to clean thebeach. A hypothetical bioethanol plant is considered in this studyin order to convert the collected macroalgae into bioethanol. Theemergy analysis highlights that nature has a strong influence onboth systems.