Cath, if you want to dip your toes in the water and chase freshwater macroinvertebrates two easy basic technical books (lots of pictures) are (i) The Waterbug Book by John Gooderham & Edward Tsyrlin (2002; with reprints every few years), and (ii) Colour Guide to Invertebrates of Australian Inland Waters by John H Hawking and Felicity J Smith (1997). They each have lists of references that will get you into the scientific literature.