A bridge is visible on "Loire-Atlantique - Orthophotos 2016 - 10 cm" imaging or on this picture
https://www.levoyageanantes.fr/wp-content/uploads/2023/01/BOC-JARDIN-DES-PLANTES-credit-Make-Me-Smile-1800x1350.jpg 
Yet I'm not sure it's fully surrounded by water.
In any case, is the use of the "islet" tag of any particular concern?