Aquatic macroinvertebrate communities are sensitive indices of stream water quality and ecological health. In the first phase of a three-year effort to conduct invertebrate-based bioassessments of urban/suburban streams within Allegheny County, Pennsylvania, chemical and invertebrate samples were collected during the spring of 2001 at 35 stations on 33 different streams. All of these stations were located near the mouths of streams tributary to the navigation pools of Emsworth Locks and Dam, Monongahela River Locks and Dam #2, and Monongahela River Locks and Dam #3.

Chemically, the study streams tended to be alkaline, hard, and mineralized. The mean values for pH, alkalinity, acidity, hardness, and conductivity were 7.79, 130.7 mg/l as CaCO3, 8.9 mg/l as CaCO3, 390.8 mg/l as CaCO3, and 1215 uhmos/cm, respectively. Calcium concentrations averaged 109 mg/l and sodium 100 mg/l. Concentrations of ammonia and metals (especially iron and aluminum) were elevated at a number of stations. These parameters are fingerprints of widespread influences of alkaline mill slag leachates, highway deicing salts, and sewage contamination, and, at some locations, acid mine drainage from bituminous coal mines.

More than 15,000 invertebrate organisms from 67 different taxa were collected, identified, and enumerated at the 35 stations. Condition scores were then developed from the invertebrate data for each station, where a score greater than 80% indicates that a stream is non-impaired, 60-79% slightly impaired, 40-59% moderately impaired, and less than 39% severely impaired. All of the 35 stream stations examined were impaired to various degrees; 42.8% severely impaired, 37.2% moderately impaired, and 20% slightly impaired. While it is disappointing that there were no streams without measurable degradation, it is still encouraging that 20% of the streams examined were only slightly impaired, and that 37.2% were moderately impaired. The diversity of aquatic life found in these streams during the first phase of the 3R-2N bioassessment exceeds what might have been expected from historical memories and impressions of these urban waterways as industrial waste conduits and/or open sewers. While no attempt was made to collect fish, they were incidentally collected during the invertebrate sampling at seven stations, and incidentally observed at eleven other stations. The seven streams that were only slightly impaired, and their condition scores, were: 1) Pine Creek, 71.3%; 2) Mingo Creek, 66.2%; 3) Dry Run, 66.2%; 4) Sandy Creek, 63.7%; 5) West Run, 62.0%; 6) Chartiers Creek, 61.3%; 7) and Guyasuta Run, 60.0%.