Aquatic ecosystem assessment is a rapidly developing field, and one of the newer approaches to assessing the condition of rivers and lakes is the Reference Condition Approach. This is a significant advancement in biomonitoring because it solves the problem of trying to locate nearby control or reference sites when studying an ecosystem that may be degraded, a problem that bedevils traditional approaches. Rather than using upstream reference sites in a river system or next-bay-over reference sites in a lake, an array of ecologically similar, least-exposed to stress sites scattered throughout a...