Venice lagoon, Italy

Venice lagoon, extending over 195 square miles (500 km2) between the Italian coast and the Adriatic Sea, is Italy’s largest wetland. A place where freshwater and saltwater meet, this marsh of silt, clay, and sand is especially rich in nutritive elements that favor the development of a multitude of aquatic species and attract many birds. The lagoon is threatened today by urban and industrial pollution, particularly hydrocarbons and heavy metals. It also holds a major concentration of phosphates and nitrates deriving from agriculture that encourage the proliferation of a green algae, Ulva rigida. This algae causes eutrophization, reduction of the oxygen content of the water, which is fatal to fish. In industrialized nations the nitrate concentration of continental waters has doubled—even quintupled in some countries—in the past thirty years.