My girlfriend and I are staying just outside Chinon for a week and I am really keen to go for a river bathe/swim, somewhere safe. A bit of a Google suggests Barrou, which is an hour or so away, but I was wondering if there's anywhere a little closer. Normally I could spend some time researching myself, but unfortunately our Internet access is a little intermittent!
This site (in French) shows 11 bathing spots in Touraine on an interactive map. These include reservoirs (plans d'eau), converted quarries, riverside beaches, as well as lakes. Here is another interesting page (in French) from the departmental website, showing swimmable areas in Touraine. Lastly according to this other website, the closest swimming location to Chinon is a riverside beach close to a camping some 11km from the town, commonly known as Baignade Camping L'Ile-Bouchard:
Le lieu de baignade le plus proche de Chinon est la plage BAIGNADE CAMPING située sur la commune de Assay, elle est à 10,7km de Chinon, qualité d'eau de baignade : Très bonne. C'est une plage de bord de rivière.
All in all it makes sense that you'd have to drive a bit to get away from the cities in order for the (river) water to be safe for swimming.
For completeness sake note that you can find more information by typing
baignade rivière chinon in your favourite search engine.