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.

Most fish species in Johnson Creek tolerate warm water and disturbed conditions.
These include red-sided shiners, sculpin, suckers, and speckled dace.

Large populations of salmon inhabited the creek before urban construction altered the watershed and the stream channel, and in the 21st century, the creek and its tributaries still provide habitat for smaller numbers of chinook and coho salmon, steelhead, and coastal cutthroat trout.
Steelhead populations in Johnson Creek are within the Lower Columbia River steelhead distinct population segment and listed as threatened (2011).
Chinook and coho salmon are listed as threatened as part of the Lower Columbia River Evolutionary Significant Unit (2011).
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.
Most fish species in Johnson Creek tolerate warm water and disturbed conditions. These include red-sided shiners, sculpin, suckers, and speckled dace.
Large populations of salmon inhabited the creek before urban construction altered the watershed and the stream channel, and in the 21st century, the creek and its tributaries still provide habitat for smaller numbers of chinook and coho salmon, steelhead, and coastal cutthroat trout. Steelhead populations in Johnson Creek are within the Lower Columbia River steelhead distinct population segment and listed as threatened (2011). Chinook and coho salmon are listed as threatened as part of the Lower Columbia River Evolutionary Significant Unit (2011).
Johnson Creek (Willamette River tributary)