⠿ Map Layer
Click any map marker to view site details & trends. Use the layer toggle (top-left of map) to visualize different parameters.
Map dot colors represent annual averages for each site and parameter. For bacteria (E. coli and Enterococcus), the dot color reflects the most recent annual geometric mean (e.g., the 2025 summer geo mean). For lab chemistry (NO₃-N, Ortho-P, Chloride, TSS), dots reflect the yearly average of all monthly samples for the most recent year with data. For water temperature and conductivity, dots show the yearly average of all field readings for the most recent year.
Bacteria data are summarized as annual summer geometric means (May–October sampling season), computed from individual grab samples collected at each site each year. Geometric means are used rather than arithmetic means because bacteria concentrations are log-normally distributed — the geometric mean better represents the central tendency of the distribution and is the standard metric used by state water quality agencies.
Grading follows the WCC State of the Watershed Methodology (2024):
| Grade | E. coli (CFU/100mL) | Enterococcus (CFU/100mL) |
|---|---|---|
| A | <126 | <35 |
| A− | 126–378 | 35–105 |
| B | 378–630 | 105–175 |
| C | 630–882 | 175–245 |
| D | 882–1,134 | 245–315 |
| F | >1,134 | >315 |
The goals on site reports are ≤126 CFU/100mL for E. coli and ≤35 CFU/100mL for Enterococcus.
Monthly grab samples are analyzed at a certified laboratory. Each point on the site trend charts represents a single monthly sample. The network-wide overview chart shows the monthly average across all actively sampled sites for that month. Standards referenced:
- NO₃-N: 3 mg/L (PADEP)
- Ortho-P: 0.1 mg/L (PADEP)
- Chloride: <50 mg/L safe; 50–120 mg/L harmful begins; 120–230 mg/L harmful; >230 mg/L most harmful (WCC standards)
- TSS: 25 mg/L (NJ WQS reference)
Water temperature and conductivity are measured in the field at each visit using a calibrated multiparameter sonde. Values shown on site reports are monthly averages of all readings taken at that site in a given month. Data come from the WCWS Field Sensor Master files (2017–2025) supplemented by field readings recorded during bacteria sampling visits.
Site rankings show the percentage of historical data points that exceed a threshold for each parameter:
- E. coli / Enterococcus: % of annual geo means at or above Grade C/D threshold
- NO₃-N & Ortho-P: % of monthly lab samples exceeding the PADEP standard
- Chloride: % of monthly samples exceeding 50 mg/L (first harm threshold)
- Water Temp: % of monthly readings exceeding 24°C
Rankings reward consistent performance over time, not just the most recent reading. A site with one very high reading will rank better than a site that chronically exceeds thresholds.
Winter road-salt surveys (January–February) measure chloride and conductivity at additional sub-basin locations beyond the regular monitoring network. These sites (designated with _A, _B suffixes) appear on the Chloride map layer and in site reports but may have limited data — only the winter snapshot readings.
- WCWS Field Sensor Master (2017–2025)
- WCWS Professional Lab Master (2018–2025)
- WCWS Bacteria Geometric Means (DE E. coli 2022–2025; PA E. coli & Enterococcus 2016–2025; DE Enterococcus 2016–2025)
- WCWA Winter Salt Snapshot (2025–2026)
- Watershed boundary: WCC_Branches.shp (University of Delaware / WCWS GIS)
- Stream network: NHD WhiteClay_Streams.shp
Dashboard built for the White Clay Watershed Association (WCWA). Data through April 2026. Contact WCWA for questions about data collection methods.