Human-caused change may be positive, neutral, or negative. Human actions that increase ecological risks range from toxic spills and excessive nutrient release in agricultural runoff to destruction and fragmentation of natural habitats and the introduction of exotic species. This behavior has left a legacy of degraded environments. This mandate clearly established a legal foundation for protecting aquatic biota. Unfortunately, the vision of biological integrity was not reflected in the act's implementing regulations.
Integrity implies an unimpaired condition, or the quality or state of being complete or undivided.
As a result, aquatic organisms and aquatic environments have declined precipitously in recent decades. Water resource programs have not and are not protecting biological integrity in the nation's waters because society continually fails to see rivers, and the landscapes they drain, in their entirety. Until an integrative perspective dominates our collective conscience, the condition of rivers will continue to decline. To implement biological criteria, managers need formal methods for sampling the biota of streams, evaluating the resulting data, and clearly describing the condition of sampled stream reaches. The complexity of biological systems, and the varied impacts humans have on them, require a broadly based, multimetric index that integrates information from individual, population, and assemblage levels.