Sea water is mild initially - so you can do this! (4)
I believe the answer is:
swim
'you can do this' is the definition.
The definition suggests a singular noun which matches the answer.
'sea water is mild initially' is the wordplay.
'initially' indicates taking the first letters.
The first letters of 'sea water is mild' is 'SWIM'.
'so' is the link.
Can you help me to learn more?
(Other definitions for swim that I've seen before include "Do the butterfly, perhaps?" , "Bathe" , "Sink or ____" , "Be immersed" , "Crawl, e.g." .)