Erica maintaining lake's physical condition (6)
I believe the answer is:
health
'physical condition' is the definition.
'health' can be an answer for 'condition' (health is a kind of condition). I'm not sure about the 'physical' bit.
'erica maintaining lake's' is the wordplay.
'erica' becomes 'heath ' (I've seen this before).
'maintaining' indicates putting letters inside.
'lake' becomes 'L' (geographical abbreviation).
'heath' going around 'l' is 'HEALTH'.
Can you help me to learn more?
(Other definitions for health that I've seen before include "It's said to be more than wealth" , "General condition of body (and/or mind)" , "Fettle -- condition" , "Freedom from illness" , "Fitness" .)