How do dams affect migrating fish and spawning fish populations?

Dams significantly disrupt the natural life cycles of migratory fish by creating physical barriers that prevent adults from reaching their spawning grounds and hinder young fish from traveling downstream to the ocean.1

To mitigate these impacts, engineers utilize fish passes, such as:

• Fish ladders: A series of stepped pools that allow fish to navigate around the dam.1
• Fish locks: A system operating like a ship lock that raises fish through the height of the dam.1

Despite these technologies, the cumulative effect of multiple dams on a single river system has often led to dramatic population declines. In some instances, such as on the Snake River, the construction of dams for hydroelectric power and navigation has been linked to the near-extinction of native spawning populations. Consequently, there is a growing ethical and environmental movement to remove certain dams, such as the former Edwards Dam on the Kennebec River, to restore river connectivity and revitalize fish populations.1