Flanking English river creature, they cross awkwardly in waders (6-8)

'waders' is the definition.
(oyster catcher is a kind of wader)

'flanking english river creature they cross awkwardly' is the wordplay.
I cannot really see how this works, but
'english' could be 'e' (abbreviation) and 'e' is located in the answer.
'river' could be 'r' (abbreviation for river) and 'r' is found within the answer.
'creature' could be 'cat' (I've seen this before) and 'cat' is found in the answer.
'cross' could be 't' (shape) and 't' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

'in' acts as a link.

Can you help me to learn more?