Good repeatedly to enter small river to fish for eels (7)

'fish for eels' is the definition.
(I've seen this in another clue)

'good repeatedly to enter small river' is the wordplay.
'good' becomes 'g' (abbreviation).
'repeatedly' indicates the doubling of some letters.
'to enter' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'river' becomes 'nile' (Nile River is an example).
'g' doubled is 'gg'.
's'+'nile'='snile'
'gg' going into 'snile' is 'SNIGGLE'.

'to' is the link.