I found this article interesting, brought to my attention from my contacts at California Fish and Game. The article is entitled "Anti-terror fish guard S.F.'s water: Bluegill monitored to detect an attack on city's drinking supply"
http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/09/06/MNG77L01H61.DTL
http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/09/06/MNG77L01H61.DTL