Carr was also known for his efforts in conservation, especially for sea turtles, helping convince Costa Rica to establish Tortuguero National Park in 1975. He was a co-founder of the Caribbean Conservation Corporation, which helps to save and monitor sea turtles in Tortuguero, Costa Rica. He often joined his wife Marjorie Carr in conservation work, as she was a major advocate for conservation in her own right. In 1952 the National Academy of Sciences awarded Carr the Daniel Giraud Elliot Medal.