The news arrived yesterday that one of Australia’s leading river ecologists, and also one of the most generous, kind and wise men I have known, died unexpectedly on Saturday 27 February. Keith Walker’s work in rivers spanned more than 40 years, much of it in the Murray-Darling Basin. For many, he was ‘Mr Murray’, because of his vast experience and knowledge of that river. He lectured and researched at the University of Adelaide for more than 30 years, and was fortunate enough to work (and publish) with Bill Williams, Jim Puckridge and many, many others. Keith edited The Ecology of River Systems (1986) with Bryan Davies and was an editor of River Research and Applications for twenty years. Keith sat on many, many committees advising on environmental issues and published more than 200 peer-reviewed and other articles. He had a long interest in freshwater mussels, and was always very happy to discuss these neglected, but important, animals. I was extremely fortunate to work closely with Keith, when we co-edited our book Ecology of Australian Freshwater Fishes (2013). His strength, tenacity and wisdom during those years, I will never forget. I learned so much, and was grateful every day to have his experience and gift for writing to guide us. His encouragement and enthusiasm never flagged, even when faced with the most recalcitrant of authors. All of those who knew Keith will miss him terribly. But we will also be grateful every day for knowing, and working with, a man such as him.