DNA in the environment, such as water and soil, is called “environmental DNA.” The recent development of environmental DNA research is remarkable. A small amount of water collected on-site allows for the detection of target organisms, as well as the collection of their biomass and genetic information, without directly capturing the organisms. Using the environmental DNA method, we can obtain big data on macro-organisms that could not be obtained by conventional methods, and it is expected to lead to the evaluation of marine biodiversity and biomass.