 Generally, metal concentrations increase downstream.A study conducted in 1999 for the City of Portland by researchers from Portland State University found that Johnson Creek had marginal conditions for macroinvertebrates, an important source of food for fish and other aquatic life.The study compared differences in these life forms and in water chemistry from two urban streams, Johnson Creek and Tryon Creek in southwest Portland, with two nearby rural streams and found that benthic communities in the urban streams were degraded compared to the regional reference creeks.