There are many thousands of beetle species in Europe. Several of these are of interest to flyfishers either because they are aquatic at some stages in their life cycle or because they get blown onto streams and lakes.
Details of many other waterside and aquatic beetles can be found in Pat O'Reilly's 245-page full-colour book Matching the Hatch.
O'Reilly, Pat. (2017) Matching the Hatch. Shrewsbury: Quiller Publishing.
Foster G. N. & Friday L. E. (1988) Key to adults of the water beetles of Britain and Ireland (Part 1). Taunton: Field Studies Council.
Harde K.W. & Severa F. (1984) Field Guide in Colour to Beetles. Littlehampton Book Services.