Links protecting river levels (5)
I believe the answer is:
tiers
'levels' is the definition.
('tier' can be a synonym of 'level')
'links protecting river' is the wordplay.
'links' becomes 'ties' (tying is a kind of linking**).
'protecting' is an insertion indicator.
'river' becomes 'r'.
'ties' going around 'r' is 'TIERS'.
(Other definitions for tiers that I've seen before include "Rows; ranks" , "More than one bank" , "Layers of rites" , "I rest in layers" , "Layers, levels" .)