Water Quality

Stream Water Quality Monitoring

The OCWA stream biomonitoring project began in 2004 and continues to this day. Stream biomonitoring involves assessment of water quality in streams using macroinvertebrates as indicators of water quality. Macroinvertebrates are invertebrate organisms large enough to see with the naked eye and include various taxa (groups) including aquatic insects, clams, snails, worms, and crustaceans. These organisms vary in their sensitivity to water pollution, with some types being extremely sensitive to pollution and others being more tolerant. The relative abundance of more- and less-sensitive species, and their diversity, provide a robust and reliable indication of the overall water quality at a given site.

OCWA is using the water quality ranking system that was developed by the NY State Dept. of Environmental Conservation (DEC) Stream Biomonitoring Unit - a methodology that has been approved by the US EPA. Because the OCWA utilizes NYS DEC methodology, the OCWA's results are comparable to the field data collected by the State. The DEC methodology results in a water quality assessment for each sampling site that is expressed numerically as water quality score called a Biological Assessment Profile, or BAP. The BAP is expressed in two ways in DEC reports: a numerical value from 0-10, where 10 equals the best possible water quality; and a narrative description. Review a more detailed description of these narrative descriptors.

When mapping this data, the OCWA typically displays the stream biomonitoring points using a unique symbol for each category: non-impacted sites are shown as green circles, slightly impacted sites are yellow squares, moderately impacted sites are orange triangles, and severely impacted sites are red pentagons.

In addition to a sample of the macroinvertebrate community, other data collected at each site include certain physical characteristics of the stream site; chemical data, including dissolved oxygen, dissolved oxygen saturation, temperature, specific conductivity, pH, salinity; digital photography; GPS coordinates; and aquatic vegetation information. Detail on the significance of these parameters as well as a glossary of terms, project history, and other information can be found in Appendix 1 of the Summary Report for Years 2004 to 2006. These parameters are provided for each site in the appendices of the reports. Older reports, maps and appendices are available upon request.

  • 2012 Quassaick Creek Watershed Stream Biomonitoring Report (Link to Watershed Initiative page)

Maps, Data and GIS Files

The Stream Biomonitoring Map below depicts the locations of the sites that have been sampled through the OCWA stream biomonitoring project from 2004 to 2012. The symbol for each site indicates the Biological Assessment Profile (BAP) for that particular site, as described in the paragraphs above. For sites that were sampled in more than one year, the symbol for the most recent year's data is shown on top. The sites are labeled with the Station ID and, for sites that have been sampled since 2009, the BAP; the BAP is color-coded by year, as indicated in the map legend.

Other Information

Impervious Cover

There have been a variety of research efforts over the years that have shown a correlation between impervious cover and water quality. In 2005 the OCWA completed the attached report that studied impervious cover, road density, land use, and population density in urban and rural areas in Orange and Rockland County, NY.