Delectable turning in a river (5)

I believe the answer is:

tasty

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'delectable' is the definition.
(I've seen this in another clue)

'turning in a river' is the wordplay.
'turning' becomes 'st' (I can't explain this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'a river' becomes 'tay' (Scottish river).
'st' going inside 'tay' is 'TASTY'.

Can you help me to learn more?

(Other definitions for tasty that I've seen before include "Having good flavour" , "With a nice flavour" , "Appetising, having pleasant flavour" , "Sexually attractive?" , "Attractive, appealing" .)

I've seen this clue in the Evening Standard.

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