In strange dialect, having big mouth? (7)
I believe the answer is:
deltaic
'having big mouth?' is the definition.
(having a river delta)
'in strange dialect' is the wordplay.
'in strange' is an anagram indicator (I've seen this in other clues).
'dialect' with letters rearranged gives 'DELTAIC'.
(Other definitions for deltaic that I've seen before include "of lower Nile region?" , "big-mouthed?" , "the mouth of the Nile maybe" .)