This verion of a unit written by the Australian Science Education project, which is preparing materials for science instruction in grades seven through ten, is available for national testing. It contains two student books, the first providing instruction for six activities considered basic to an understanding of the aquatic habitat, and reading on gaseous and energy exchange, and on aquatic food webs. The second student book outlines nine optional activities that students may choose to follow. The options include study of the "quality" of fresh water, the variations in habitat within a river, fish hatcheries, and sewage treatment. Most options involve student experiment or information retrieval. There is a separate workbook for use during a pond excursion, including drawings of representative organisms likely to be found. A test booklet contains 28 self-check multiple choice questions, with reference to appropriate sections of the materials if remedial work is needed. The Teachers Guide provides an overview of the unit, suggestions for organizing study, lists of apparatus needed, and suggested sources of reference material. (AL)