Women tend to have lower interest in engineering as compared to men, which previous research has shown is partly explained by gender differences in self-efficacy, social belongingness and communal career goals. Therefore, to attract more women to engineering, effective interventions are needed that target these factors. In this study, we evaluated an industry-designed intervention for high school students. The intervention consisted of a two-day interdisciplinary course on water issues and careers in the water sector, located by a lake in the Swedish countryside. The participating 722 high school students answered a survey before, immediately after, and three months after the intervention. We measured interest, self-efficacy, social belongingness, communal career goal affordance, and stereotype threat, in relation to engineering. The results showed expected gender differences in all pre-measures. A promising result was that the intervention raised women’s engineering self-efficacy and social belongingness and reduced stereotype threat levels. However, repeated exposure might be necessary for the changes to last. Engineering interest was unexpectedly not affected by the intervention, which may imply that stronger increases in self-efficacy and social belongingness are necessary to impact interest.