Seaside Sussex
Some French campsites only allow men to wear speedos in their swimming pools instead of apparently unhygienic Bermuda style trunks. We discovered this after a particularly long and hot journey to a campsite near St Rémy de Provence. My husband resorted to wearing my M & S pants as he didn't have any speedos (which looked better on him than they do on me) but he did get to cool off in the pool. So speedos are highly recommended.
This was our expectation too but of the 5 sites with pools we've just returned from, this rule was not evident.