Dr. Heinz G. Stefan died at the age of 89 on November 4, 2025.  He had a distinguished career at the University of Minnesota in the USA and was well-known worldwide, having been an author of over 240  refereed journal articles and numerous  technical reports, review articles, and book chapters. He gave more than 60 invited lectures and taught abroad in India, China, and Brazil for weeks at a time. He received a number of academic awards, including the International Water Association Founders Award for Best Paper in Water Research, the American Society of Civil Engineers’ Hunter Rouse Award, and the University of Minnesota’s Distinguished Graduate and Professional Educator Award.

In addition to his scientific accomplishments, Dr. Stefan advised, inspired and mentored more than 100 masters  and PhD students during his career, many of whom have become engineers, researchers and faculty members exploring  and implementing fundamental scientific principles  to better understand and protect  aquatic ecosystems. He was one of a handful of academics worldwide to lead the civil engineering discipline into the important new research area of environmental hydraulics.  His impact on the field was widely felt through the early leadership that he demonstrated, through the strength of the research that he performed, and through the number of his students that found important and influential positions throughout the world.  

From his early investigations of thermal discharges to his later work on water quality modeling and the effects of global warming on aquatic systems, Dr. Stefan’s research advanced both fundamental science and applied engineering. Perhaps his most significant contribution to the field was the development of a thermal and kinetic energy model of lakes and reservoirs, which expanded the use of these models to include wind effects on stratification and spawned a number of models used today by government agencies, consulting firms, and universities, including his own MINLAKE model. Today, nearly all modern lake and reservoir water quality models build upon the thermal stratification concepts pioneered by Dr. Stefan and his students. Over his career, he further expanded this area of research and modeling to include the fate and transport of environmentally important chemicals such as phosphorus and oxygen, the water quality impacts of road salt, and the effects of global warming on fish habitat to better guide practioners charged with water quality improvement of our  streams, lakes, and reservoirs.

His legacy endures not only in the models, equations, and methods he developed but also in the generations of scientists and engineers he nurtured. Through his lifelong dedication to understanding and protecting aquatic ecosystems, Dr. Heinz Stefan profoundly shaped the science of environmental hydraulics and the stewardship of our planet’s waters.

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