208 Region 2 - 305(b) Integrated Report Water Quality Trends

208 Region 2 - 305(b) Integrated Report Water Quality Trends, 2002-2026
NFRWQPA · 208 Planning Region 2 · Phase 1 prototype · historical edition

208 Region 2 - 305(b) Integrated Report Water Quality Trends, 2002-2026

Is water quality in Larimer and Weld counties improving? Trends from the CDPHE 305(b) and Integrated Report cycles 2002–2026 (2002, 2006, 2008, 2010, 2012, 2016 and 2018–2026), measured as the share of assessed miles or acres that fully attain their uses, and as the number of 303(d)-listed parameters.

Map

Click a segment or lake to drill down to its AUID.

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Share of assessed miles by IR category

303(d) parameters

Bar = % of the area's assessed miles listed for the parameter at the end of the period. Color = change since the start: green improved, red degraded, yellow no change, gray never listed 2018–2026.

Designated use attainment, end of period

Fully supportingNot supporting (incl. T, TMDL)Insufficient info / not assessed

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, the period spanned by the 2018–2026 Integrated Report cycles (each cycle assesses roughly the five prior years of data). Low-flow years leave less dilution for point and nonpoint loads, so read the 303(d) trends against these flows.

Precipitation, Larimer and Weld counties

NOAA NCEI county averages · water year (Oct–Sep) totals, inches

Each 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, the period spanned by the 2018–2026 Integrated Report cycles. Dry years cut runoff and dilution; wet years raise stormwater and nonpoint loads.

Larimer CountyWeld County

About the data

County clipping

Assessment units are included when at least 5% of their mapped length or area falls in Larimer or Weld County. Each unit's size is its full segment size in the workbook multiplied by its in-county share. Units split in 2026 (for example COSPBT14_A, COSPCP21_A, COSPMS05c_A) are counted through 2024 and replaced by their child units in 2026.

Historical cycles (2002–2016)

Digitized from the 2002, 2006, 2008, 2010, 2012 and 2016 305(b) reports in the Association's files. Before about 2016 the Division assessed whole segments (for example COSPCP13a_1000) rather than today's AUIDs. Each old segment is matched to the current Region 2 units with the same sub-basin, segment number and water type and given their in-county share; Big Thompson, Cache la Poudre and Laramie segments with no current match are counted fully in Region 2, and other unmatched segments (mainly Lower South Platte below the Weld–Morgan line) are left out. The 2002 report uses the 1998 303(d) list and lists only assessed segments. On the map and in the AUID table, values marked * are the former segment's status.

Use support

Not Supported and T-tmdl values are shown as not supporting. T-tmdl appears as "not supporting, TMDL" (T), as in the Division's dashboards.

QC corrections applied

The 2026 status of three AUIDs follows NFRWQPA's QC review (November 2026), which the source workbook does not yet carry. Dissolved iron is added to the 2026 303(d) List for COSPBT07_A; the workbook had it under the retired COSPBT07_B. Selenium is removed from COSPBO07b_B. COSPMS07_C (Horse Creek Reservoir) moves from Category 5 to 3b, with aquatic life insufficient data, pH removed and chlorophyll-a on the M&E List.

Data sources

Every dataset used in this dashboard
# Dataset Used for Source Coverage
1 NFRWQPA “2026 August 20 Uses & Segments Calculations 2026 UPDATE” workbook (Protected Uses sheet) Primary compilation of the Division's IR results for each AUID: categories, use support, 303(d), TMDL and M&E listings, segment sizes Association file 2018–2026 IR cycles
2 CDPHE WQCD Integrated Water Quality Monitoring and Assessment Reports (305(b)/303(d)), 2018, 2020, 2022, 2024 and 2026 cycles Source reports behind the workbook; all attainment and parameter trends CDPHE Impaired Waters ↗ 2018–2026 IR cycles
3 CDPHE WQCD Status of Water Quality in Colorado / 305(b) and Integrated Reports, 2002, 2006, 2008, 2010, 2012 and 2016 (use support and use attainment appendices) Historical segment sizes, use support, IR categories and causes of impairment for the 2002–2016 cycles Association files, C:\NFRWQPA\Claude\305b Reports and Reg 93 Reports 2002–2016 (no 2004 or 2014 report)
4 Colorado 1998 Section 303(d) List (Appendix A of the 2002 305(b) report) 303(d) parameters for the 2002 cycle Association file, 2002 305b IR-Tables.pdf 1998 list
5 WQCD 2026 Integrated Report, Appendix C delisting table Parameters removed from the 303(d) list in 2026; used to check the workbook CDPHE Impaired Waters ↗ 2026 cycle
6 5 CCR 1002-93, Regulation No. 93: Colorado's Section 303(d) List of Impaired Waters and Monitoring and Evaluation List 303(d) and M&E listings by cycle (2026 rule effective 03/30/2026, with archived versions) Colorado Code of Regulations ↗ 2018–2026 versions
7 5 CCR 1002-38, Regulation No. 38: Classifications and Numeric Standards, South Platte River Basin Segment descriptions and designated use classifications (rule effective 12/31/2025) Colorado Code of Regulations ↗ Current rule
8 CDPHE 2026 segmentation geodatabase (Streams2026, Lakes2026) AUID river lines and lake polygons on the map; in-county share of each unit CDPHE Impaired Waters (GIS data) ↗ 2026 segmentation
9 U.S. Census Bureau county boundaries (us-atlas, 1:10 million) Larimer and Weld county outlines; county clipping of AUIDs us-atlas (Census cartographic boundaries) ↗ Current
10 NFRWQPA 2026 Integrated Report story map dataset (GIS\StoryMap) Association's processed version of the sources above, clipped to Larimer and Weld counties; the direct input to this dashboard Association files, C:\NFRWQPA\Claude\GIS\StoryMap 110 AUIDs, 2018–2026
11 USGS National Water Information System: site and annual statistics services Gauge locations, drainage areas and water-year annual mean discharge (parameter 00060) for 10 gauges: 06752260, 06752280, 06752000, 06741510, 06738000, 06730525, 06725450, 06720990, 06721000, 06754000 USGS Water Services ↗ WY1996–2025; retrieved Oct 20, 2026
12 NOAA NCEI Climate at a Glance, county time series (nClimGrid) Water-year (October–September) precipitation totals for Larimer County (CO-069) and Weld County (CO-123) NOAA Climate at a Glance ↗ WY1995–2025; retrieved Oct 20, 2026
13 CDPHE Integrated Report story maps (2022, 2024, 2026) Layout and assessment framework the dashboard follows Colorado's 2026 IR story map ↗ Framework only, no data
14 NFRWQPA 208 Region 2 WQ Trending GIS Study RFP (draft, October 3, 2025), including CSU (Tyler Wible) review comments Assessment levels, AUID list, parameter list, trend rules, trend icons, disclaimer text and pie-chart suggestion Association file, C:\NFRWQPA\Claude Scope document
15 ChatGPT session summary cited in the RFP The water quality improvement claim this dashboard tests; not used as data Shared AI session ↗ Claim tested, not a data source
16 Map rendering: Leaflet 1.9.4 (open-source) Interactive map display; no basemap tiles are used leafletjs.com ↗ Software
17 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

Disclaimer. Water quality trend variables are affected by the Water Quality Control Division's corrections for errors, resegmentation, reclassification, and changing standards over time. AUIDs are added, deleted, split, and redescribed between cycles, so assessed miles and acres change from cycle to cycle. Trends here compare each cycle's share of the area's assessed size, not a fixed set of segments.

Method notes. Fully attaining = IR Category 1 (1a/1b). Impaired = Category 4a or 5. The Division used Category 2 (some uses attaining, others not assessed) through 2018 and dropped it from 2020 on, so jumps in "fully attaining" across 2018→2020 mostly reflect that change; 2002 and 2006 categories are derived from use support (all uses fully supporting = 1, any not or partially supporting = 5, a mix of supporting and not assessed = 2, none assessed = 3). No 2004 or 2014 report has been digitized, so bars skip those cycles. Region 2 sizes are the in-county portion of each AUID (see About the data); the watershed level uses each AUID's full size. Phosphorus is represented by chlorophyll-a listings (nutrient response); Fecal coliform listings (1998) are grouped with E. coli; biological listings ("Aq Life", "Bugs") with macroinvertebrates. TSS, BOD and uranium have no 303(d) listings in these cycles. Sources: see Data sources above. Streamflow: USGS National Water Information System annual statistics (water years 1996–2025); several gauges were discontinued by USGS and are shown for their period of record only. Recent years may include provisional data. Precipitation: NOAA National Centers for Environmental Information, Climate at a Glance county time series (nClimGrid), October–September totals, water years 1995–2025.