Photo by Sherman Morss Jr.
The Boston Harbor Islands have a humid maritime climate that supports an assemblage of plants and animals typical of coastal New England. The climate of the islands offers a particular attraction to visitors when hot, humid weather dominates the region. The modulating effect of surrounding waters typically produces significantly cooler temperatures in contrast with the city and its suburbs. Inversely, winter temperatures on the islands are warmer than those of mainland sites. The Boston Harbor Islands are in a Class II Area as defined by the Clean Air Act. Natural coastal processes, especially northeast storms, continue to reshape the island landforms.
Today, Boston Harbor is vastly cleaner than it had been for decades. As is typical of many coastal areas near major metropolitan centers, the harbor had been used for waste disposal since colonial times. Sewage from 43 municipalities now undergoes state-of-the-art primary and secondary treatment at Deer Island. Sludge is removed and the effluent is disinfected and dechlorinated and is ready to be discharged through a 9.5-mile outfall tunnel. The effluent is mixed with the deep waters of Massachusetts Bay.