A Decree of the Supreme Court of the United States, entered in 1954, established the position of Delaware River Master within the U.S. Geological Survey. In addition, the Decree authorizes diversions of water from the Delaware River Basin and requires compensating releases from certain reservoirs, owned by New York City, to be made under the supervision and direction of the River Master. The Decree stipulates that the River Master will furnish reports to the Court, not less frequently than annually. This report is the 52nd Annual Report of the River Master of the Delaware River. It covers the 2005 River Master report year; that is, the period from December 1, 2004, to November 30, 2005. During the report year, precipitation in the upper Delaware River Basin was 7.56 in., or 117 percent of the long-term average. Combined storage in Pepacton, Cannonsville, and Neversink Reservoirs remained high from December 2004 to May 2005 and reached a record high level on April 3, 2005. Reservoir storage decreased steadily from May to early October, then increased rapidly through the end of November. Delaware River operations throughout the year were conducted as stipulated by the Decree. Diversions from the Delaware River Basin by New York City and New Jersey were in compliance with the Decree. Reservoir releases were made as directed by the River Master at rates designed to meet the flow objective for the Delaware River at Montague, New Jersey, on 120 days during the report year. Releases were made at conservation rates-or rates designed to relieve thermal stress and protect the fishery and aquatic habitat in the tailwaters of the reservoirs-on all other days. During the report year, New York City and New Jersey complied fully with the terms of the Decree, and directives and requests of the River Master. As part of a long-term program, the quality of water in the Delaware Estuary between Trenton, New Jersey, and Reedy Island Jetty, Delaware, was monitored at various locations. Data on water temperature, specific conductance, dissolved oxygen, and pH were collected continuously by electronic instruments at four sites. In addition, selected water-quality data were collected at 3 sites on a monthly basis and at 19 sites on a twice-monthly basis.