Mobile hospital crossing river in swamp (5)
I believe the answer is:
marsh
'swamp' is the definition.
(I've seen this before)
'mobile hospital crossing river' is the wordplay.
'mobile' becomes 'mas' (I am not sure about this - if you are sure you should believe this answer much more).
'hospital' becomes 'H' (abbreviation for hospital).
'crossing' is an insertion indicator (to cross can mean to go over or around).
'river' becomes 'r' (abbreviation).
'mas'+'h'='mash'
'mash' placed around 'r' is 'MARSH'.
'in' is the link.
Can you help me to learn more?
(Other definitions for marsh that I've seen before include "Quagmire" , "Wetland" , "Waterlogged land" , "Low-lying wet land with grassy vegetation" , "Bog, swamp" .)