Counters scuba failing amid rising waters (8)
I believe the answer is:
abacuses
'counters' is the definition.
(I've seen this before)
'scuba failing amid rising waters' is the wordplay.
'failing' indicates an anagram (a failed spelling of the word).
'amid' is an insertion indicator.
'rising' says the letters should be written in reverse (in a down clue, letters go up).
'waters' becomes 'sea' (the sea is water).
'sea' backwards is 'aes'.
'scuba' is an anagram of 'bacus'.
'bacus' put within 'aes' is 'ABACUSES'.
(Other definitions for abacuses that I've seen before include "Calculating devices" , "Counters" , "Count on these" , "old computing devices" , "outdated calculators" .)