Dr. Patrick, who in 1996 received the nation’s highest award for scientific achievement, began focusing on ecology at a time when the dangers of pollution barely pierced the national consciousness. Women were so rare in the sciences that when she sought a job at the Academy of Natural Sciences in 1934 — the same year she received a doctorate in botany from the University of Virginia — she was told she would not be paid. She was also advised not to wear lipstick to work.
It was about seven years before she earned a salary years at the academy. She became, in 1973, the first female chair of the academy’s board of trustees.
“My great aim,” Dr. Patrick once told the Philadelphia Inquirer, “has been to be able to diagnose the presence of pollution and develop means of cleaning things up.” Her research on limnology — the study of freshwater rivers and lakes — meant wading into an estimated 850 rivers and streams worldwide. Her work drew scientific and political attention to the problem of water pollution, and she later became one of the early scientists to speak out about global warming.
“She’s one of the few early women in limnology, and so she was a great role model — really a pioneer, when most universities didn’t even have female professors in the sciences,” said Deborah Bronk, the past president of the Association for the Sciences of Limnology and Oceanography, which awards a prize named in Dr. Patrick’s honor. “She was also a real pioneer in using research findings and advocating for public change” in environmental causes.
Dr. Patrick’s work led Congress to pass the 1972 Clean Water Act, which she helped write. Groundbreaking in its time, it remains the chief federal law focused on reducing and preventing water pollution. She advised Presidents Lyndon B. Johnson and Ronald Reagan on environmental issues.
Her chief contribution was identifying the significance of the diatom, now a key measure of water pollution. In the 1930s, when she was completing her doctoral research, Dr. Patrick was the first scientist to focus on this single-celled organism, eaten by other underwater creatures, that is present in almost every freshwater environment.
Earlier scientists had simply measured chemical levels to describe the health of bodies of water. Dr. Patrick found that measuring the presence of the diatom, a simple and prevalent life form — and using a tool she invented called a diatometer — gave a much better picture of the health of the ecosystem’s life forms. The belief that biodiversity is the chief indicator of water health is now known as the Patrick Principle.
“She was looking at this at a time long before the general public or the government was interested in matters of water pollution,” said Bob Peck, a senior fellow at the Academy of Natural Sciences. “When the environmental crisis began to emerge in the 1970s, she was the dominant figure in the field of water pollution.”
Ruth Myrtle Patrick was born Nov. 26, 1907, in Topeka, Kan., and raised in Kansas City, Mo. She took weekly nature walks with her father, a lawyer who had once aspired to a career in science.
“I remember the feeling I got when my father would roll back the top of his big desk in the library and roll out the microscope,” she told an interviewer in 2004. “He would make slides with drops of the water samples we had collected, and I would climb up on his knee and peer in. It was miraculous, looking through a window at a whole other world.”
At 7, she once recalled, her father gave her a microscope with the instruction: “Don’t cook. Don’t sew. You can hire people to do that. Read and improve your mind.” She was a 1929 graduate of Coker College in Hartsville, S.C.
In 1931, she married married entomologist Charles Hodge IV, who, according to the Inquirer, once described life with Dr. Patrick as “like being married to the tail of a comet.” At the time of their nuptials, Dr. Patrick’s father made a request.
“I would like you to let Ruth keep her name,” he said. “I want the name Patrick to amount to something in science.”
Hodge died in 1985. Her second husband, Lewis H. Van Dusen Jr., died in 2004. Survivors include a son from her first marriage, Charles Hodge V of Fairway, Kan.; three stepchildren, Duncan Van Dusen of Bryn Mawr, Pa., Michael Van Dusen of Washington and Sally Johnson of Philadelphia; 15 grandchildren; and 18 great-grandchildren.
From 1933 to 2003, Dr. Patrick published more than 200 papers and contributed to books. She taught botany and limnology at the University of Pennsylvania for more than 35 years. After studying the water quality near DuPont chemical plants, she became an adviser to the company on environmental issues and, in 1975, was named the first woman on its board of directors.
At a White House ceremony in 1996, President Bill Clinton awarded her the National Medal of Science.
Until she turned 97, Dr. Patrick worked five days a week at the Academy of Natural Sciences, whose limnology center is named in her honor. At 100, she still came in to her office to work on her multi-volume text “Rivers of the United States,” whose installments ran up to 900 pages.
“Many of the things that we take for granted now, in terms water quality and water purity, would not be where they are without her,” Peck said. “Ruth Patrick always tried to apply what she was studying to broader social concerns and helped to make the work relevant. She thought that, ultimately, the reason for studying all this was to help to improve human life and the life of the natural world.”