Pose holding large fish, crossing river to find narrow shelter (4,6)

'narrow shelter' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'pose holding large fish crossing river' is the wordplay.
I cannot quite understand how this works, but
'large' could be 'l' (eg in clothes sizes) and 'l' is present in the answer.
'pose' could be 'sit' (sitting is a kind of posing) and 'sit' is located in the leftover letters.
'fish' could be 'trench' and 'trench' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...

'to find' acts as a link.

Can you help me to learn more?