Thomas Hill Res. Nr. Dam Lake is a 3,500-acre productive, nutrient-rich eutrophic lake in Randolph County, Missouri. Water quality is graded D based on 3 sampling years through 2025. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 6 other monitored lakes in Randolph County, Thomas Hill Res. Nr. Dam Lake ranks #6 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 | F |
| Phosphorus | 61 µg/L | D |
| Chlorophyll-a (Algae) | 14.2 µg/L | C |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 3,500 acres |
| Public Access | Yes |
Where to stay near Thomas Hill Res. Nr. Dam Lake
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Fishing Thomas Hill Res. Nr. Dam Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
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 |
Recreation & Access
Water Temperature
Thomas Hill Res. Nr. Dam Lake averages about 83°F at the surface in summer, usually warmest in Aug (about 86°F) and coldest in Jun (about 79°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 18 field readings (2021–2025) via the EPA Water Quality Portal. See the full Thomas Hill Res. Nr. Dam Lake water temperature breakdown →
Location
County Ranking
Ranked #6 of 7 lakes in Randolph County
Cleaner Lakes Within 30 Miles
Thomas Hill Res. Nr. Dam Lake holds Grade D. 5 nearby lakes hold higher grades.
- BLake Nehai TonkayeaChariton County · 13.3 mi · Two grade letters higher (D → B)
- COld ReservoirRandolph County · 13.6 mi · Higher grade (D → C)
- CRothwell LakeRandolph County · 13.6 mi · Higher grade (D → C)
- CThomas Hill Lake @ Hwy TMacon County · 4.9 mi · Higher grade (D → C)
- DSugar Creek LakeRandolph County · 11.2 mi · Higher overall water quality score
Nearby Lakes in Randolph County
Explore Thomas Hill Res. Nr. Dam Lake across LakeGrade
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Other Grade D Lakes in Missouri
Eutrophic Lakes in Missouri
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More records, surveys & data sources
Reservoir Info (USACE NID)
Thomas Hill Res. Nr. Dam Lake is a man-made reservoir impounded by the Thomas Hill Reservoir Dam (completed 1966), built primarily for flood risk reduction on the MIDDLE FORK CHARITON RIVER; earth-type dam, 70 ft tall and 2,450 ft long.
- Surface area
- 3,500 ac
- Normal storage
- 70,000 ac-ft
- Max storage
- 260,458 ac-ft
- Drainage area
- 146.88 sq mi
- Hazard class
- High
- Owner
- ASSOCIATED ELECTRIC CORP
All listed purposes: Flood Risk Reduction;Recreation.
Source: USACE National Inventory of Dams, NID ID MO10134 · Operator website · Matched by proximity (0.39 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Thomas Hill Res. Nr. Dam Lake under Clean Water Act (NPDES) discharge permits, including 2 classified by the EPA as major dischargers. 2 facilities have a reported Clean Water Act violation in the past three years.
- Aeci Thomas Hill Energy CenterClifton Hill · 1 mi away · NPDES MO0097675MajorRecent violation
- Thomas Hill - Mining DivisionClifton Hill · 2.5 mi away · NPDES MO0003948MajorRecent violation
- Aeci Thomas Hill Closed FacilityClifton Hill · 0.3 mi away · NPDES MO0139874
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2025-08-14
Monitoring stations: 2