Got lower in part of pool, conserving energy (8)
I believe the answer is:
deepened
'got lower' is the definition.
'part of pool conserving energy' is the wordplay.
'part of pool' becomes 'deepend' (area in a swimming pool).
'conserving' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'deepend' going around 'e' is 'DEEPENED'.
'in' is the link.
(Other definitions for deepened that I've seen before include "Made more intense" , "Became more profound" , "Made more profound" .)