Crossword Genius

Boundaries one first organised to include river (9)

Ross

I believe the answer is:

frontiers

'boundaries' is the definition.
(I know this)

'one first organised to include river' is the wordplay.
'organised' is an anagram indicator.
'to include' is an insertion indicator.
'river' becomes 'r' (abbreviation).
'one'+'first'='onefirst'
'onefirst' is an anagram of 'fontiers'.
'fontiers' enclosing 'r' is 'FRONTIERS'.

(Another definition for frontiers that I've seen is " Countries' borders".)

I've seen this clue in The Guardian.
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