Health Highlights: Aug. 24, 2004 Here are some of the latest health and medical news developments, compiled by editors of HealthDay:    -----      Contaminated Fish in Many U.S. Lakes and Rivers      Fish that may be contaminated with dioxin, mercury, PCBs and pesticides are swimming in more than one-third of the United States' lakes and nearly one-quarter of its rivers, according to a list of advisories released by the Environmental Protection Agency...