Possible Clues:

• It gets its turn in 8 down
• Percival Lowell "discovery"
• Place for a low bridge
• Structure with locks
• Locks in a tin with a pound
• That's dug by way of water
• Ottawa Region's Rideau______
• Man-made channel of water
• Able to get to a half-century by way of water
• Is a half-century able to hold water this way?