Background Deoxyribonucleic acid (DNA) is the hereditary material in organisms that contains the biological instructions for building and maintaining them. The chemical structure of DNA is the same for all organisms, but differences exist in the order of the DNA building blocks, known as base pairs. Unique sequences provide a means to identify individual species and detect their presence within aquatic or terrestrial environments. Environmental DNA (eDNA) is nuclear or mitochondrial DNA that is shed from an organism into the environment. Sources of eDNA include feces, mucous, and gametes; shed skin; and carcasses. In aquatic environments, eDNA is diluted and distributed by currents and other hydrological processes....