Splash and support little swimmer (7)
I believe the answer is:
tadpole
'little swimmer' is the definition.
(I've seen this before)
'splash and support' is the wordplay.
'splash' becomes 'tad'.
'and' is a charade indicator (letters next to each other).
'support' becomes 'pole' (poling is a kind of supporting).
'tad'+'pole'='TADPOLE'
(Other definitions for tadpole that I've seen before include "Embryonic frog" , "A frog-to-be" , "Young amphibian" , "wriggler?" , "Aquatic larva of frog or toad" .)