Donald W. Pritchard, a pioneering oceanographer who spent 50 years studying the Chesapeake Bay, died of a stroke April 23 in Severna Park, Md. He was 76.

He served both as first director of Johns Hopkins' Chesapeake Bay Institute and first chairman of Hopkins' oceanography department, which he founded in 1950.

His lasting contributions to the science of estuaries also included a sensitivity to ways humans could minimize their impact on the environment.

Over the years, he won several environmental awards for his work and was the first recipient of the Mathias Medal, named for Maryland's former U.S. senator Charles Mathias, honoring Pritchard's scientific work on the bay.

He was known as a scientist, inventor and theoretician throughout his career. Although he left Hopkins in 1979, he continued to devote his energies to marine sciences for the remainder of his life. He worked at the State University of New York at Stony Brook until 1988, and at the time of his death, he was adjunct professor at the University of Maryland. He and a colleague reportedly had been writing shortly before his death a paper comparing the Chesapeake Bay to the Long Island Sound.

Pritchard served in World War II as a meteorologist, forecasting wave conditions on the beaches of Normandy for the D-Day invasion.

He is survived by his wife, Thelma Lydia Pritchard; two daughters, Jo Anne Mitchell of Severna Park, Md.; two sons, Donald W. Pritchard Jr. of Severna Park and Albert Pritchard of Harwood, Md.; a sister, Virginia Comstock of Santa Ana, Calif.; 11 grandchildren; and three great-grandchildren.