Water clarity in the black sludge plume was often zero. Aesthetics are important, but water clarity also has a major impact on marine ecosystems. Many important species of plants, including seagrasses, require adequate light. If poor water clarity means insufficient light penetrates to the seafloor, where seagrasses are rooted, the plants will die off. When this happens, the bottom sediments are no longer bound and stabilized by the roots, and can be more easily stirred up, further exacerbating poor water clarity.
Natural turbidity is highest in spring through fall.
Other natural sources of suspended solids include particles brought in by rivers, and sediments stirred up into the water by storms or normal wave action. In Boston Harbor, water clarity varies from region to region, with the clearest water found at the mouth of the harbor. More cloudy waters occur in shallow regions like Dorchester and Quincy Bays, where bottom sediments are easily resuspended. Eventually, water clarity should improve so that the areas of seagrasses can expand from their limited habitat in Hingham Bay to other areas of the harbor. These toxic materials adversely affect sensitive marine organisms by inhibiting growth and reproduction.