A former West Australian surf life saving club instructor has been charged with historic sexual assault offences.

Police allege the 25-year-old man sexually assaulted a 15-year-old girl over several months in 2010 when he was an instructor.

He has been charged with four counts of aggravated sexual penetration without consent and one count of indecent dealing with a child under the age of 16.

The man is due to appear in Perth Magistrates Court on Friday.