This book aims to bridge the gap between ecotoxicology and limnology. The intended readers of the book are water managers, policy makers with a scientific background as well as researchers/advisors in the area of water management. The book provides an ecotoxicological perspective on lake management and describes eutrophication of shallow, temperate lakes. It surveys the influence of toxic substances (e.g., agricultural pesticides) on the aquatic ecosystem, especially the relation between algae and daphnids. The message of the book is that nutrients such as phosphorus are not the only important factor in explaining and managing eutrophication: toxic disturbance of to-down control is also an important factor to be considered. The results of extensive studies and experiments (some unpublished) on lake eutrophication are presented in this book.