Course Introduction: https://www.fba.org.uk/identification-freshwater-invertebrates-species-level-distance-learning-course
The Freshwater Biological Association's distance learning course: "The Identification of Freshwater Invertebrates to Species Level". The three introductory modules and 9 taxon-group modules can be downloaded from their website.
The individual parts cover all groups of freshwater macro-invertebrates and give useful hints on preserving, examining and identifying. They also include details of recent additions to our fauna which are obviously absent from reference guides published prior to their discovery.