What effect would the construction of a dam have on a river ecosystem?

The construction of a dam can significantly disrupt a river ecosystem by altering water flow and temperature, which can affect aquatic habitats and species. It may block the migration of fish and other organisms, leading to population declines. Additionally, the creation of a reservoir can inundate terrestrial habitats, while sediment accumulation behind the dam can reduce nutrient flow downstream, impacting the overall health of the ecosystem. Overall, these changes can lead to decreased biodiversity and altered ecological balances.