Water makes the river what and where it is. All life needs water. People often talk about the earth's life being carbon-based (mostly). True, but even more it is water-based! Most life forms are composed of at least 80% water. In addition, aquatic plants and animals live part or all of their lives within, on, or by the water. Long-term, of course, there must be change with climate change, for example, when most of Britain was covered by ice some 10,000 years ago, the vegetation under that ice was not what is there today. No vegetation is therefore, in the exact sense, stable. But what about lesser time periods-5, 15, 50, 150 years ago? For how long has the vegetation remained stable? Unfortunately there is a lack of recorded history so this small book will summarize some of what is available, but its main aim is to inform, encourage, and pave the way for new interest. It is worth noting that THE HABITAT CHOOSES THE SPECIES. It is easy to think the plant chooses, in reality the plant's choice is very limited. This book is a demonstration, for students and naturalists alike, of changes and the sensitivity of river communities to their environment, and indeed of the speed of their response.