Biological Conditions

The health of fish and macroinvertebrate (i.e., animals without backbones that are larger than the size of a pencil dot) communities is a strong indication of overall stream health.

Since the mid–1990’s many natural resources professionals working in the Anacostia watershed have monitored these communities using an Index of Biotic Integrity or IBI approach. The IBI compares the fish and macroinvertebrate communities of urban streams with those of healthy reference streams, incorporating geographical, ecosystem, community, and population, as well as distribution and abundance variables that account for differences in waterbody size, type, and region of occurrence.

The table on the right shows adjusted IBI scores and verbal ratings for the Anacostia River and its tributaries. While there are still many gaps in the Anacostia macroinvertebrate and fish community IBI databases, available data have proven extremely valuable in the restoration effort.
Fish Macroinvertebrates
Scores Verbal Rating Scores Verbal Rating
47 - 50 Excellent 36 - 40 Excellent
35 - 46 Good 27 - 35 Good
23 - 34 Fair 17 - 26 Fair
0 - 22 Poor 0 - 16 Poor

Click on the following links for graphs showing biological conditions in the Sligo Creek subwatershed.

The adjusted Fish IBI score puts the overall health of the Sligo Creek subwatershed fish community in the Poor range.

The adjusted Macroinvertebrate IBI score puts the overall health of the Sligo Creek subwatershed macroinvertebrate community in the Poor range.