Maybe dam Russian river, dry banks beginning to crack (8)
I believe the answer is:
obstacle
'maybe dam' is the definition.
(I know that dam is a type of obstacle)
'russian river dry banks beginning to crack' is the wordplay.
'russian river' becomes 'Ob' (river in Russia).
'dry' becomes 'stale' (similar in meaning).
'banks' indicates putting letters inside (bank can mean to surround or border).
'beginning to' suggests taking the first letters.
The initial letter of 'crack' is 'c'.
'stale' placed around 'c' is 'stacle'.
'ob'+'stacle'='OBSTACLE'
(Other definitions for obstacle that I've seen before include "Anything that stands in the way" , "Hindrance, obstruction" , "hold-up" , "Maybe let" , "Block to progress" .)