After graduating from the Sunset Hill School for girls in Kansas City, Mo. (now Pembroke Hill School), Ms. Patrick resisted her mother’s wishes that she marry and learn the social graces and decided to study botany instead. Enrolling at Coker College in Hartsville, S.C., she went on to earn a bachelor’s degree in the subject in 1929 and then a master’s and a doctorate in the same field at the University of Virginia. She received her Ph.D. in 1934.

She began her association with the Academy of Natural Sciences, which had the best collection of diatoms in America, as a graduate student in 1933. In 1937, she became an assistant curator of microscopy, an unpaid position. Only in 1945 was she put on the payroll, and two years later she established the limnology department, now called the Patrick Center for Environmental Research. She was its chairwoman until 1973, when she was named to the Francis Boyer chair of limnology. From 1973 to 1976 she was chairwoman of the academy’s board.

Her breakthrough came in 1948, when she led a study of Conestoga Creek in Lancaster County, Pa., to obtain data on the relationship between diatoms and water quality. The creek was chosen because it suffered from many types of pollution, including sewage, fertilizer runoff, toxic substances and metals from industry.

Her team, including a chemist, a bacteriologist, and animal and plant experts, determined the types of pollutants in sections of the river and then identified the plant and animal species. Dr. Patrick found that some species of diatoms thrived in water that was heavily contaminated with organic material like human sewage, while other flourished among chemical pollution.

Refining this finding, she was able to examine a sample of stream water under a microscope, determine the type and numbers of diatoms present, and tell what kind of pollution was present and how severe it was.

To check the number and types of diatoms, Dr. Patrick invented a device called the diatometer, a plastic box containing microscope slides that when strategically placed in a stream collects the maximum number of the organisms.

More broadly, her results showed that under healthy conditions, many species of organisms representing different groups should be present.