For three generations pollution of the Delaware has been self-evident. However, up to now there has never been available a detailed analysis of that pollution; what it is, who is responsible for it, what might be done, and what it would cost to abate it. In 1957-58, at the request of the Corps of Engineers, the Public Health Service made a preliminary study of pollution in the Delaware Estuary. This in turn led to the making of the comprehensive study covered by the report. The study was begun in 1961 by the Water Supply and Pollution Control Division of the Public Health Service, now the Federal Water Pollution Control Administration, at the request of the state and interstate pollution control agencies. This is a preliminary report of that study.