Randolph County, Missouri · Water Quality Report Card
Thomas Hill Reservoir
Thomas Hill Reservoir in Randolph County, Missouri has a water quality grade of D (Poor). Water clarity: 2.3 ft visibility. Phosphorus: 61 µg/L. Chlorophyll-a (algae): 14.2 µg/L.
- Clarity
- 2.3 ft
- Mean depth
- ~65 ft est.
- Type
- Eutrophic
- Trend
- ↑ Improving
Thomas Hill Reservoir is a productive, nutrient-rich eutrophic lake in Randolph County, Missouri with an estimated average depth of about 65 feet. Water quality is graded D based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. Compared to the 6 other monitored lakes in Randolph County, Thomas Hill Reservoir ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2025-08-14. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D (Poor)
Very murky, less than 2.3 ft of visibility. Phosphorus level: 61 µg/L. Chlorophyll-a: 14.2 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | |
| Phosphorus | 61 µg/L | Poor |
| Chlorophyll-a (Algae) | 14.2 µg/L | Fair |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~65 ft est. |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Missouri has not published bathymetry for Thomas Hill Reservoir.
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Fishing Thomas Hill Reservoir
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.095 m/yr | 3 |
| Phosphorus | ↑ Improving | -1.63 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +2.99 µg/L/yr | 5 |
Location
County Ranking
Ranked #7 of 7 lakes in Randolph County
Cleaner Lakes Within 30 Miles
Thomas Hill Reservoir holds Grade D. 3 nearby lakes hold higher grades.
- ALake Nehai TonkayeaChariton County · 13.3 mi · Two grade letters higher (D → A)
- COld ReservoirRandolph County · 13.6 mi · Higher grade (D → C)
- CRothwell LakeRandolph County · 13.6 mi · Higher grade (D → C)
Nearby Lakes in Randolph County
Explore Thomas Hill Reservoir across LakeGrade
More Missouri Lake Rankings
Other Grade D Lakes in Missouri
Eutrophic Lakes in Missouri
More records, surveys & data sources
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Where this data comes from
67 measurements from 2 monitoring stations, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC64 samples · 2021–2024 - Missouri Dept. of Natural Resources
MDNR3 samples · 2025
Analytical methods
- Depth, Secchi disk in meters
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- Nitrogen and Phosphorus, Total, Whole-water, Alkaline Persulfate Digest
- Turbidity by Nephelometry
Monitoring station identifiers (2)
Grade thresholds come from the U.S. EPA National Lakes Assessment 2022 Technical Support Document (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated.
Data Sources
Water quality data from the EPA Water Quality Portal
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2025-08-14
Monitoring stations: 2