The perilous home of some clingy midge larvae
ELC2159 Spécimen déposé à l'herbier MT Eau libre, dans un marais riverain, sur sol limoneux épais. Avec Ludwigia palustris, Eleocharis palustris, Brasenia shreiberi et Eleocharia acicularis.
Rainbow Springs
Pretty sure this is correct. I could not get to the plant to get a better look. The submersed leaves are narrow (but probably more than 4mm wide) and linear. They appear to have bands on either side of the midrib.