I think Donacia vulgaris.
In pool of water under SS Great Britain, Bristol.
Habitus insgesamt; Femur bis Hinter-Rand Flügeldecken mit Doppelzähnchen - Männchen.
Habitus, Femur to edge of Elytra with double teethies - male.
Diving beetle - Swansea Community Farm invertebrates walk City Nature Challenge, Buglife/ Natur am Byth