Related Clues:

• Mother among mammals
• Get blocked up
• Barrier
• Mica, for one
• Folk dancer's shoe, perhaps
• Grand Coulee, for one
• Classic British war film, "The ___ Busters"
• Reservoir's edge
• Beaver job
• Dutch shoe
• Hydroelectric option
• Footwear that's hard to run in
• Mica or Gardiner
• Beavers' construct
• Lake former, perhaps