The Mediterranean has been described as the world’s largest swimming pool. However, it can also be described now as the world’s dirtiest sewer, full of rubbish, oil, chemicals and waste of all kinds. Unfortunately, most countries bordering the Mediterranean differ greatly in their attitudes to this problem. While some countries want to start cleaning up the Mediterranean, others have begun building new ports to develop their oil wells and natural gas fields. Industries have now grown in all the countries surrounding the Mediterranean. It will take a century for all the water in the Mediterranean to drain into the Atlantic Ocean, and be replaced by clean water. Three great rivers, the Nile, Po, and Rhone, all flow into the Mediterranean, carrying lots of pollutants into the sea and making it very dangerous for everyone who swims in the Mediterranean and who catches fish there.