There are two national-level databases that compile results of water quality monitoring in aquatic environments throughout Japan: the Comprehensive Information Website for Water Environment managed by the Ministry of the Environment (https:// waterpub.env.go.jp/water-pub/mizu-site/) and the Water Information System managed by the Ministry of Land, Infrastructure, Transport and Tourism (). However, the reported quantification limits for metals in these databases are not sufficiently low to be used for ecological risk assessments, and measurements at a majority of monitoring sites have either not been performed or fall below the reported limits. For instance, the reported quantification limits for Cu, Cd, and Pb are generally higher than 10, 0.3, and 1 μg/L, respectively, which are close to or approximately an order of magnitude higher than the U.S. EPA hardness-adjusted water quality criteria for aquatic life (e.g., 2.3, 0.21, 0.42 μg/L at water hardness of 30 mg/L; U. S. Environmental Protection Agency (2016); U.S. Environmental Protection Agency ( )).