Comes out again at lake and joins up with it (9)

'comes out again' is the definition.
('emerges' can be a synonym for 'comes out' so perhaps 'reemerges' is OK for 'comes out again')

'lake and joins up with it' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
The remaining letters 'remerges' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'at' is the link.

Can you help me to learn more?