A swimming coach committed an obscene act with one of his charges, a 12-year-old boy, at a public pool toilet after his class ended.

Tan Koek Seng, now 68 and jobless, was jailed for 10 months yesterday after he was found guilty of sexual exploitation under the Children and Young Persons Act for the 2015 incident.

Calling him "a menace to society", Deputy Public Prosecutor Chee Ee Ling said: "There is a public interest in protecting children attending lessons at public facilities from unwarranted sexual advances.''

Tan was convicted last month, after a four-day trial, of committing the obscene act in a cubicle of the toilet at Hougang Swimming Complex in Hougang Avenue 4 on Feb 8, 2015.

The prosecution called 14 witnesses to prove its case, but the victim and his mother did not testify.

The investigation officer said that the mother refused to allow her son to testify in court. Both were unwilling to relive the trauma.

The gist of the prosecution's evidence against Tan was based on the positive statements he made to the police in March and July that year.

Yesterday, DPP Chee asked the court to impose at least 15 months' jail, saying Tan was more than five decades older than the victim, and had abused the trust reposed in him.

She said Tan lacked remorse and his acts caused "significant harm'' to the victim and his mother, as the investigation officer had testified.

Pleading for leniency, Tan, who was unrepresented, said he was suffering from a heart condition and was due for cataract surgery in September.

He could have been fined up to $10,000 and/or jailed for up to five years.