Coastal and marine areas have huge ecosystem values. However, intensive anthropogenic activities have largely changed coastal landscapes. In this research investigation, sediment and water samples were collected to clarify the distribution patterns and sources of heavy metals in the rapid growing urbanization areas of Haizhou Bay in China’s Jiangsu Province. The physical and chemical properties of the water and sediment were tested. Meanwhile, the ecological toxicity levels of heavy metals were also examined using the I_geo accumulation index, and the potential ecological risk index (PERI), respectively. The results revealed that the water and sediments of the marine ecosystems had an unpolluted status, with the element concentrations not exceeding the threshold effect levels. In terms of the spatial distribution patterns of the heavy metal concentrations in the water samples, it was determined that the Cd concentration was only 0.10 μg/L in the western area, and the highest concentration value was found in the northeastern area. The concentration levels of As in the sediments exhibited higher concentrations mainly in the southern area of Haizhou Bay. The results obtained in this study can help increase the awareness of the mitigating actions that coastal areas naturally provide against pollution and also provide valuable information for the design of future plans and policies that will progress toward a more sustainable development of the such areas.