Prescott, G.W., 1979
How To Know the Freshwater Algae
Although the book is about American algae, most genera and species are widely dispersed so it is still of use in our area.
The major part of the book consists of a long dichotomous key (going up to couplet 719 - is this a record?) with a discussion of each genus as it keys out. The index includes a pictorial glossary.
The 1954 edition is downloadable from archive.org