Loch Mary Reservoir
Hopkins County, Kentucky148 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Mesotrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #3 of 4 in the county
- 29 ft max depth
- Public access
- Limited data
Loch Mary Reservoir in Hopkins County, Kentucky has a water quality grade of B (Good). Phosphorus: 22.1 µg/L. Surface area: 148 acres.
- Max depth
- ~29 ft est.
- Area
- 148 acres
- Type
- Mesotrophic
- Phosphorus
- 22.1 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Watch Loch Mary Reservoir’s letter
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Loch Mary Reservoir is a 148-acre mesotrophic lake in Hopkins County, Kentucky with an estimated average depth of about 29 feet. Water quality is graded B based on 1 sampling years through 2019. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 3 other monitored lakes in Hopkins County, Loch Mary Reservoir ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, KY DOW, last sampled 2019-09-04. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The B is nutrients and algae, not a swimming clearance. Loch Mary Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: B (Good)
No clarity data. Phosphorus 22.1 µg/L. TSI 49. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 22.1 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 49 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~29 ft est. |
| Average Depth | ~11 ft est. |
| Surface Area | 148 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Kentucky has not published bathymetry for Loch Mary Reservoir.
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.
Fishing Loch Mary Reservoir
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +3.3 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Loch Mary Reservoir is a man-made reservoir impounded by the Loch Mary Reservoir Dam (completed 1950), built primarily for water supply on the Clear Creek; earth-type dam, 27 ft tall and 1,300 ft long.
- Surface area
- 148 ac
- Normal storage
- 1,450 ac-ft
- Max storage
- 2,350 ac-ft
- Drainage area
- 3.67 sq mi
- Hazard class
- High
- Owner
- CITY OF EARLINGTON
Source: USACE National Inventory of Dams, NID ID KY00148 · Operator website
EPA Impairment Status
Loch Mary Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit KY-1171 · Official waterbody report
County Ranking
Ranked #3 of 4 lakes in Hopkins County
Nearby Lakes in Hopkins County
Frequently asked questions about Loch Mary Reservoir
Where is Loch Mary Reservoir?
- Loch Mary Reservoir is a lake in Hopkins County, Kentucky. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Loch Mary Reservoir?
- Loch Mary Reservoir in Hopkins County, Kentucky has a water quality grade of B (Good). Phosphorus: 22.1 µg/L. Surface area: 148 acres.
Is Loch Mary Reservoir safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Loch Mary Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Loch Mary Reservoir?
- No published bathymetric survey covers Loch Mary Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 29 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 148 acres.
Explore Loch Mary Reservoir across LakeQuality
More Kentucky Lake Rankings
Other Grade B Lakes in Kentucky
Mesotrophic Lakes in Kentucky
Where this data comes from
12 measurements from 2 monitoring stations, 2016–2019. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- KY WQX
21KY_WQX12 samples · 2016–2019
Analytical methods
- Phosphorus by Colorimetry
- Total Phosphorus After Block Digestion
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)