The continuing deterioration of the Mediterranean’s natural environment is largely due to human activity and is linked to the large concentration of people along coastal zones and to tourism. The main threats are: – Sewage and urban runoff. Of the Mediterranean’s 601 coastal towns with populations of more than 10,000, only 69 percent have waste processing plants. – Urban solid waste dumped in illegal landfill sites; rubble or waste dumped in the sea covering the seabed. – Chemical industries or mining activity in coastal areas, producing toxic waste. – Systematic urbanization of the coast leading to loss of biodiversity. – Eutrophication, a frequently encountered phenomenon in enclosed bodies of water such as ports and small gulfs surrounded by built-up areas. – Shipping activities responsible for polluting the sea with crude oil. Between 1990 and 2005, 80,000 tons of petroleum ended up in the Mediterranean Sea as a result of accidents or shipwrecks. – Biological invasions. The introduction of exotic species of plants through ballast waters, fouling, import and invasion has sometimes led to catastrophic effects on the natural environment – Increasing appearance of Harmful Algal Blooms (HABs). In Greece, Italy and France the effects, in the form of ecosystem changes and effects on human health, are estimated to cost 329 million euros per year. – Overexploitation of fisheries resources. Overfishing leads to a loss of species and reduces biodiversity.