Related Clues:

• River formation
• Hoover ___
• Fort Peck ___, in Montana
• Water container?
• Spill checker?
• River part
• Gatehouse site
• Area at a river's mouth
• It can hold its water
• Lake maker, perhaps
• Block, in a way
• Block up
• Southwest alternative
• Flood preventer
• Hoover or Tarbela, e.g.