Rodents metres below river covered in hard frozen water (5,4)

'rodents' is the definition.
(house mouse is a kind of rodent)

'river covered in hard frozen water' is the wordplay.
'river' becomes 'ouse' (Yorkshire river).
'covered in' is a charade indicator (letters next to each other) (some letters go on top of or cover others).
'hard' becomes 'h'.
'frozen water' becomes 'mice' (I can't explain this - if you can you should believe this answer much more).
'ouse' put after 'h' is 'house'.
'house'+'mice'='HOUSE MICE'

'metres below' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?