Wood Mike found in river (6)
I believe the answer is:
timber
'wood' is the definition.
(I know that timber is a type of wood)
'mike found in river' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'found in' means one lot of letters goes inside another.
'river' becomes 'tiber' (River Tiber in Italy).
'm' placed within 'tiber' is 'TIMBER'.
(Other definitions for timber that I've seen before include "Wood for building, etc" , "Sawn wood" , "The tree's falling!" , "Deal possibly" , "Wood (that may be shivered?)" .)