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The construction of the weir and lock was necessary to protect the new developments on the canal ( the metropolitan railway , the tributary canals and later the harbour and ships ) from floods and ice , but also to maintain sufficient water in the canal so that ships could pass .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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