What I see floating in a great expanse of water (5,3)
I believe the answer is:
white sea
'water' is the definition.
(I know that White Sea is a inlet)
'what i see floating' is the wordplay.
'floating' indicates anagramming the letters (float can mean fluctuate or oscillate).
'what'+'i'+'see'='whatisee'
'whatisee' anagrammed gives 'WHITE SEA'.
'in a great expanse of' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for white sea that I've seen before include "Inlet of the Arctic" , "Russian waters" , "A quantity of salt water" .)