Untreated, or raw sewage, is 99.99% water, but the impurities in the remaining .01% can cause illness or death and render a stream devoid of life. Sewage treatment has meant the rebirth of Philadelphia's rivers. Decomposing sewage once consumed most of the oxygen in the rivers, leading to the death of fish and other aquatic life. Now, with sewage removed from the rivers, oxygen and fish have returned. Over the years, all three of the City's sewage treatment plants have received gold awards by the Association of Metropolitan Sewerage Agencies. - from PWD's Water and Drainage History course. © 2015 Philadelphia Water Department.