References
- Andrews , William A. 1972 . A Guide to the Study of Freshwater Ecology , New Jersey : Prentice-Hall, Inc. .
- Forest Service, U.S. Department of Agriculture . 1973 . Teaching Materials for Environmental Education , Edited by: Washington , D. C. U.S. Government Printing Office .
- Needham , James G. and Paul , Needham R. 1962 . A Guide to the Study of Fresh Water Biology , San Francisco : Holden-Day, Inc. .