The concentration of total mercury [Hg] in waters, sediments and biota (carp and crabs) as well as the concentration of methyl mercury [MeHg] in biota from upstream (surface water systems) and downstream (coastal and estuarine systems) areas within coastal watersheds along the Chinese Northern Bohai and Yellow Seas were investigated. In most waters tested, the [Hg] could have adverse effects on coastal wildlife. Based on the Chinese water quality standards for mercury, 67% of upstream waters cannot be used for agriculture or recreation. Furthermore, 53% of downstream waters cannot be used as harbors or for industrial development. The [Hg] in 3% of sediments from the Wuli and Luanhe Rivers were sufficient to cause adverse effects on ecosystems. The [Hg] in 41% of downstream crabs and the [MeHg] in 29% of downstream crabs were higher than the limits for human consumption set by the Chinese government. In all abiotic and biotic samples, only the downstream carp from the Northern Yellow Sea had a [Hg] or [MeHg] higher than those from the Northern Bohai Sea. Industrialization and urbanization were the primary sources of mercury contamination in the aquatic ecosystems studied. (C) 2012 Elsevier B.V. All rights reserved.