Canton Atoll has a single passage between the ocean and lagoon and has conspicuous environmental gradients from that passage to the back lagoon. These gradients include the physiography of the lagoon floor, water quality, and the diversity and abundance of corals, fishes, and mollusks. The gradients can apparently be attributed either directly or indirectly to circulation and water motion within the lagoon. Those oceanographic characteristics can, in turn, be attributed to the geological history of the atoll, including some human modification of the pass configuration. In addition to the studies of the atoll lagoon characteristics of the groundwater system are noted. Evidence from isolated standing water bodies on the atoll demonstrates that these features show considerable variability, which may be attributed to a combination of the immediately previous history of these bodies as well as to the physiography of the atoll.