Barcelona and surrounding cities reach about 4 million habitants. Along the coast there are tourism activities, recreational and commercial harbours, some fisheries, waste effluents and two waste water treatment plants. Near the coast human activities are mainly urban activities with some industries. In the rivers watersheds there are heavy industries and agriculture.
The main source of anthropogenic contamination in the Barcelona continental shelf was till recently the Besós River. A wastewater treatment plant was installed near the river mouth in order to decrease this impact. The plant has been discharging a mixture of solids and liquids produced in its digestion tanks (sewage sludge) through a pipeline since 1979. The coast receives discharges from the Besòs River, and the Llobregat River with a mean water discharge of 5 and 20 m3/s respectively. However the water discharge of both rivers is extremely variable (maximum values of more than 2000 m3/s in strong flood events). Both rivers traverse urban, industrial and rural settings and the watershed size is 5000 km2 for Llobregat and 1000 km2 for Besòs. The watershed near the coast is all urban. During rain events, the coast receives the impact of urban drainage storm collectors, besides that from the rivers.
It necessary some project to reduce or avoid the problem :
Construction of a new Wastedisposal Plant: primary treatment, and new waste water emissary: 3 Km from the coast and at 50 meter depth, before was 600 m off and at 20 m depth
Implementation to a secondary treatment.
Construction of a new harbor, remodelation and amplification of the old harbor, construction of several protection dikes and underwater barriers.