As urbanization accelerates, a growing influx of pollutants enters the sea through land runoff, posing a threat to coastal ecosystems. In this study, we systematically determined the concentrations of nutrients and heavy metals in the water and sediments of coastal areas (Yantai, China) and assessed their sources and ecological risks. The results showed that inland rivers transported large amounts of NO₃⁻ and PO₄³⁻ into coast water, which caused severe eutrophication. Regarding heavy metals, copper dominated in seawater, whereas plumbum and arsenic were dominant in sediment, which was sourced from aerosol deposition and mariculture. Zinc, chromium, copper, mercury, and cadmium contributed slightly to pollution, with low enrichment factors, mainly from natural sources. Further analysis showed that zinc, mercury, copper, and arsenic were significantly affected by the grain size composition in sediment. Ecological risk assessment indicated that the coastal zone of Yantai City is in a state of light heavy-metal pollution.