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The present study emphasised the speciation and mobility of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) in sediments of the Yundang Lagoon catchment (YLC) at Xiamen in China. The maximum total metals concentrations of Cr, Cu, Zn, Cd, and Pb were higher than the class I pollution level of China Marine Sediment Quality values. Average total metals concentrations of Cu, Zn, Cd, and Pb were greater than world average shale values. The highest average percentages of Cr (68.01%), Mn (39.14%), Ni (61.32%), and As (74.09%) were found in the residual fraction, while Cu (50.69%) was the highest in the oxidisable fraction. Furthermore, the greater percentages of Zn (37.65%), Cd (48.98%), and Pb (47.52%) were bound in the reducible forms in YLC sediment. Total organic carbon (TOC) showed a strong correlation with heavy metal fractions, suggesting that TOC could be a carrier of heavy metals within alkaline urban sediment. The risk assessment code values for Cd, Mn, and Zn indicate that these metals could pose a medium to a high potential risk to the aquatic organisms. However, the present remediation strategy should be continued with more focus on reducing urban runoff and domestic discharge into the lagoon. [ABSTRACT FROM AUTHOR]