The sharing of explicit images has become "commonplace" at Welsh colleges, the education watchdog has revealed.
An Estyn report said college leaders in Wales did not have a "clear picture of the extent of sexual harassment" among students.
It said fear of not being taken seriously was among the reasons students tended not to report incidents.
The Welsh government said any form of sexual harassment was unacceptable.
Estyn's report was written in response to requests by the education minister and the Senedd's children, young people and education committee.
The inspectorate visited all 12 further education colleges in Wales to interview staff and pupils and carried out an online questionnaire.
It found peer-on-peer sexual harassment among 16-18-year-olds was "complex and widely under-reported".
