Although mudflat ecosystem may be influenced due to environmental impacts of terrestrial and coastal waters, there has been little information on these impacts on bivalves in wetlands. This study aims to investigate the impact of coastal environments on bivalves in riverine and coastal wetlands. We conducted field measurements of bivalves, water and sediment environments in Edogawa and Arakawa Rivers in 2010, in which a large-scale blue tide appeared around the head of Tokyo Bay. The results reveal that the wet weight of bivalves in the coastal wetland (Sanbanze) decreased more appreciably due to the blue tide than those in riverine wetland of the Edogawa River. Furthermore, we discussed the sediment and water environments at the station where the number of the bivalves in the riverine wetland increased after the blue tide.