208 Region 2 Physical In-Stream Water Quality Trends
208 Region 2 - Physical In-Stream Water Quality Trends 2002-2026
Is the water in Larimer and Weld counties getting cleaner? This edition skips the paper record and tests what was measured in the stream. Results from the Water Quality Portal (USGS, CDPHE, Colorado River Watch, Metro Water Recovery and others) are compared with the current Regulation 38 numeric standards for each segment, in five-year data windows that line up with the 2002–2026 Integrated Report cycles.
Map
Click a segment, lake or monitoring site to drill down to its AUID.—
Share of miles by measured status, per cycle window
Parameters exceeding Regulation 38
Bar = % of the area's monitored miles where measured data exceed the parameter's Reg 38 standard in the end window. Color = change since the start window: green improved, red degraded, yellow no change, gray never exceeded in this area. The number on the right of each row is how many AUIDs had enough data to assess.
Designated use, measured, end of period
Stream vs. 303(d) list
For each parameter, AUIDs in this area are sorted by whether the end-of-period 303(d) list (Regulation 93, from the original dashboard) names the parameter and whether measured data in the matching window exceed the Reg 38 standard. "Exceeds, not listed" points to emerging problems or to data the Division did not use. "Listed, now meets" points to possible delisting candidates or to recovery.
Segments receiving permitted discharges
Active CDPHE permits (Effective or Administratively continued) for facilities in Larimer and Weld counties, from the Division's permit extract of 10/6/2026, plus the Region 2 POTWs located just outside the counties. Each permit is placed on a 2026 AUID using its outfall coordinates and the stream segment named in the permit. Each AUID shows its 2026 Integrated Report category and its measured status against Reg 38 in 2021–2025. Pick a permit type below; click a row or a map symbol to open the AUID.
2026 IR vs. measured, AUIDs receiving this permit type
Permits of this type
POTW list location check · the Association's POTW list compared with the verified AUID and the CDPHE permit status
Assessment units in this area
Streamflow at USGS gauges
Annual mean discharge by water year (Oct–Sep), cubic feet per second. Bars above the record median are blue (wetter), below are amber (drier). The shaded band marks water years 2018–2025. Low-flow years leave less dilution for point and nonpoint loads, so concentrations measured in dry windows run higher; read the exceedance trends against these flows.
Precipitation, Larimer and Weld counties
NOAA NCEI county averages · water year (Oct–Sep) totals, inchesEach county's bar is its area-averaged precipitation for the water year; dashed lines mark each county's 1995–2025 average. The shaded band marks water years 2018–2025. Dry years cut runoff and dilution; wet years raise stormwater and nonpoint loads.
How the in-stream assessment works
Data windows
Each cycle is paired with the five calendar years before it: the 2026 window is 2021–2025, 2024 is 2019–2023, and so on back to 2002 (1997–2001; the portal export starts in 2000, so the 2002 window holds only 2000–2001). Windows overlap the way the Integrated Report periods of record do.
One yardstick
Every window is scored against the same standards: the Regulation 38 tables effective 12/31/2025 for each AUID's segment. Holding the standards and the 2026 AUID boundaries fixed means a change in the trend reflects a change in the water, not a change in the rules, segmentation or listing decisions.
Sites to AUIDs
Stream sites are snapped to the nearest 2026 AUID line within 250 m and lake sites to the lake polygon within 300 m, using the CDPHE 2026 segmentation geodatabase. All sites in an AUID are pooled. Quality-control samples are dropped, results are rolled up to one value per site per day (daily maximum for temperature, daily minimum for DO, daily minimum and maximum for pH, daily mean otherwise), and lake samples deeper than 2 m are left out.
Exceedance rules
Chronic standards: the 85th percentile of the sample-to-standard ratios is above 1. DO and pH: the 15th percentile is below the minimum, or the 85th above 9.0. Acute standards and temperature daily maximums: more than one exceedance and more than 5% of samples. Water supply sulfate, chloride, dissolved iron and manganese: the median. E. coli: any two-month geometric mean (two or more samples) above 126 per 100 mL. Total phosphorus and lake chlorophyll a: the annual median (rivers) or July–September mean (lakes) above the value in two or more years. At least four samples are needed to assess a test.
Table value standards
Hardness-based metals (Cd, Cu, Pb, Mn, Ni, Ag, Zn) use the Regulation 31 TVS equations with each sample's same-day hardness (or 2.497·Ca + 4.118·Mg), falling back to the window median and capped at 400 mg/L. Ammonia uses the pH- and temperature-dependent TVS. Temperature uses the segment's tier daily maximum by season. Non-detects count as below the standard when the reporting limit is at or under it and are left out when it is above.
What is not scored
Uranium ("varies", see 38.5(3)), fish-tissue mercury, macroinvertebrates, sediment, TSS and BOD have no in-stream physical-chemical test here. Phosphorus standards marked as applying only above listed facilities, DO spawning criteria and BLM copper outside the published values are not applied. Arsenic's 0.02 µg/L total recoverable standard sits below most reporting limits, so any detection exceeds it.
Data sources
Every dataset used in this dashboard| # | Dataset | Used for | Source | Coverage |
|---|---|---|---|---|
| 1 | Water Quality Portal, Result (physical/chemical) profile, Larimer and Weld counties, stream sites (“Larimer and Weld resultphyschem” and Weld “resultphyschem” workbooks) | All measured stream results: field parameters, nutrients, ions, metals, E. coli | waterqualitydata.us ↗ | 2000–2025; 500 stream sites and 144 lake sites in Region 2 AUIDs |
| 2 | Water Quality Portal, Result profile, Larimer and Weld counties, lake/reservoir sites (same characteristics) | Measured lake and reservoir results | waterqualitydata.us ↗ | 2000–2025; retrieved Oct 23, 2026 |
| 3 | Water Quality Portal, Station service, Larimer and Weld counties | Site names, types and coordinates | waterqualitydata.us ↗ | Retrieved Oct 23, 2026 |
| 4 | 5 CCR 1002-38, Regulation No. 38: Classifications and Numeric Standards, South Platte River Basin (effective 12/31/2025) | Segment classifications and the numeric standards each AUID is scored against | Association file, C:\NFRWQPA\Claude\Regulation 38; Colorado Code of Regulations ↗ | Current rule |
| 5 | 5 CCR 1002-31, Regulation No. 31: Basic Standards and Methodologies for Surface Water (table value standards) | TVS equations for hardness-based metals, ammonia and temperature tiers; interim phosphorus and chlorophyll values | Colorado Code of Regulations ↗ | Current rule |
| 6 | CDPHE 2026 segmentation geodatabase (Streams2026, Lakes2026) | AUID lines and lake polygons; joining monitoring sites to AUIDs | Association file; CDPHE Impaired Waters ↗ | 2026 segmentation |
| 7 | Region 2 Water Quality Trends 2002–2026 (the paper-record dashboard) and its sources: NFRWQPA Uses & Segments workbook, 305(b)/IR reports, Regulation 93 | AUID list, in-county sizes, map geometry and the 303(d) listings in the Stream vs. 303(d) comparison | Association file | 2002–2026 cycles |
| 8 | NFRWQPA ArcGIS Hub, Treatment Plants layer (TreatmentPlants/FeatureServer/0) | Facility locations, permit numbers and capacities for the permitted-discharge section | NFRWQPA 208 Boundaries ↗ | 86 facilities; retrieved Nov 2, 2026 |
| 8a | EPA ECHO facility and detailed facility reports (CWA) | Second source for facility coordinates and permit status | EPA ECHO ↗ | Retrieved Nov 2, 2026 |
| 8a2 | CDPHE Water Quality Control Division active permit extract (“10-6-2026 Active Permits for Website”) | Active permits by type, permit stream segment, outfall coordinates, major/minor and status for the permitted-discharge section | Association file (CDPHE extract) | Extract dated 10/6/2026 |
| 8b | NFRWQPA 2024 208 AWQMP data inventory sheets; “POTW List” (Association) | Discharge locations and receiving segments stated by each entity; the list being checked | Association files, FILE ROOM\208 AWQMP Updates\2024 Update | 2024 update |
| 8c | USGS National Water Information System annual statistics | Water-year annual mean discharge for 10 gauges | USGS Water Services ↗ | WY1996–2025 |
| 9 | NOAA NCEI Climate at a Glance, county time series (nClimGrid) | Water-year precipitation, Larimer (CO-069) and Weld (CO-123) | NOAA Climate at a Glance ↗ | WY1995–2025 |
| 10 | Map rendering: Leaflet 1.9.4 (open-source) | Interactive map; no basemap tiles are used | leafletjs.com ↗ | Software |
| 11 | NFRWQPA QC review of 2026 AUID attributes (LarimerWeld_AUID_2026_attributes-MT QC TRACKING.csv) | Corrections to 2026 status for COSPBT07_A, COSPBO07b_B and COSPMS07_C | NFRWQPA | 2026 cycle |