Swimmers swim on vacation, including exercise by river (5)

'swimmers swim on vacation including exercise by river' is the definition.
I can't tell whether this defines the answer.

'swim on vacation including exercise by river' is the wordplay.
'on vacation' says to hollow out the word (remove centre letters) (after the inside letters have vacated the word).
'including' means one lot of letters goes inside another.
'exercise' becomes 'pe' (Physical Education).
'by' says to put letters next to each other.
'river' becomes 'r' (abbreviation for river).
'swim' with its middle taken out is 'sm'.
'pe'+'r'='per'
'sm' going around 'per' is 'SPERM'.

Can you help me to learn more?