PHILADELPHIA — A scientist whose research on freshwater ecosystems led to groundbreaking ways to measure pollution in rivers and streams has died. Ruth Patrick was 105.

Patrick is credited with creating an approach that assesses the health of a lake, stream or river by evaluating the quantity, diversity and health of its plants, insects, fish and other organisms — not solely examining the chemistry of the water itself.

Patrick also devised a tool to detect water pollution by measuring microscopic algae called diatoms. She was the recipient of dozens of the nation’s top science awards, including the National Medal of Science.