Final answer:
Dam removals in Maine are motivated by the need to restore ecological balance in river ecosystems, particularly by enhancing fish diversity and improving water quality.
Step-by-step explanation:
The primary motivation for recent dam removals in the Kennebec and Penobscot Rivers in Maine is due to a shift in the understanding of the ecological value of free-flowing rivers and the recognition that many dams no longer serve the beneficial functions they were originally intended for. Dam removal helps restore naturally fluctuating water levels, leading to increased fish diversity and improved water quality. Specifically, in the Pacific Northwest, dam removal projects aim to boost salmon populations, a keystone species, while on the Atlantic coast, dam removal has facilitated the return of anadromous fish species' migration for spawning.