?This book examines the impacts of radionuclides released from the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on inland aquatic environments. The focus is on the dynamics of radiocesium in inland aquatic environments. The book comprises three parts: migration behavior of radiocesium in river and lake environment, accumulation of radiocesium into organisms in freshwater, and integrated environmental analysis in a lake system and a forest-freshwater system. Many studies on the dynamics of radionuclides have been published after the FDNPP accident, especially of radiocesium (134Cs 137Cs) in land and marine environment. The key features of this book are the new data of freshwater environment including transport of radionuclides in river and lake watershed, and accumulation of radiocesium in freshwater fishes and insects. Another feature of this book is that it summarizes the dataset of a model lake, Lake Akagi-Onuma, from geochemical andbiological approaches. Readers will learn the actual dispersion behavior of radionuclides released from the Fukushima accident and their impacts on freshwater environments since the accident in 2011. The book presents valuable information for assessing the impacts of the FDNPP accident on ecosystem and human health, which are also useful in developing countermeasures for similar accidents and environmental contaminations.