The Hoover Dam and Lake Mead have been associated with which ecological change?

• A. Inverse estuary formation due to reduced freshwater inflow
• B. Increased flood events
• C. Creation of tidal pools
• D. Expansion of coral reefs

Answer: (A)

The main idea here is how large dams and reservoirs change the balance of freshwater and seawater in coastal environments. Damming the Colorado River and creating Lake Mead reduce the amount of freshwater reaching downstream estuaries, and the arid climate with high evaporation concentrates salts. With less freshwater input, seawater can dominate more of the estuary and push farther upstream, raising salinity levels inland. This shift creates an inverse estuary, where the estuary becomes saltier than the adjacent seawater under certain conditions.

That’s why this option fits best: it links the dam and reservoir operation to reduced freshwater inflow and the resulting higher salinity inland, which characterizes an inverse estuary. The other ideas don’t align with what the dam system typically causes—dams generally lessen floods, not increase them; tidal pools and coral reef expansion aren’t tied to this inland dam and reservoir scenario in the same way.