Start to drain river — modified dam lower? A fantastic vision (5-5)

I believe the answer is:

dream-world

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'a fantastic vision' is the definition.
The definition suggests a singular noun which matches the answer.

'start to drain river modified dam lower?' is the wordplay.
'start to' indicates taking the first letters.
'modified' is an anagram indicator.
The initial letters of 'drain river' is 'dr'.
'dam'+'lower'='damlower'
'damlower' with letters rearranged gives 'eamworld'.
'dr'+'eamworld'='DREAM-WORLD'

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I've seen this clue in The Times.

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