Charles Mill Reservoir is a 1,350-acre highly nutrient-loaded hypereutrophic lake in Ashland County, Ohio. Water quality is graded F based on 1 sampling years through 2021. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings.
Source: EPA Water Quality Portal sampling records, Ohio DNR, last sampled 2021-10-11. Grade methodology: LakeGrade methodology.
Watch Charles Mill Reservoir water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 0.9 ft of visibility. Trophic State Index: 79.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 0.9 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 79 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 1,350 acres |
| Public Access | Yes |
Where to stay near Charles Mill Reservoir
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Fishing Charles Mill Reservoir
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +5.72 m/yr | 2 |
Recreation & Access
Water Temperature
Charles Mill Reservoir averages about 78°F at the surface in summer, usually warmest in Aug (about 79°F) and coldest in Oct (about 65°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 135 field readings (2010–2021) via the EPA Water Quality Portal. See the full Charles Mill Reservoir water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Charles Mill Reservoir, reaching a maximum surveyed depth of 27 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Ohio DNR.
County Ranking
Ranked #1 of 1 lakes in Ashland County
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Other Grade F Lakes in Ohio
More records, surveys & data sources
Reservoir Info (USACE NID)
Charles Mill Reservoir is a man-made reservoir impounded by the Charles Mill Dam (completed 1936), built primarily for flood risk reduction on the BLACK FORK OF MOHICAN RIVER; earth-type dam, 52 ft tall and 1,390 ft long.
- Surface area
- 1,350 ac
- Normal storage
- 7,400 ac-ft
- Max storage
- 88,000 ac-ft
- Drainage area
- 215 sq mi
- Hazard class
- High
- Owner
- USACE - Huntington District
All listed purposes: Flood Risk Reduction;Fish and Wildlife Pond;Recreation.
Source: USACE National Inventory of Dams, NID ID OH00020 · Operator website
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
4 EPA-permitted facilities operate within about 5 miles of Charles Mill Reservoir under Clean Water Act (NPDES) discharge permits. 4 facilities have a reported Clean Water Act violation in the past three years.
- Charles Mill Lake CampgroundMansfield · 0.4 mi away · NPDES OH0146650Recent violation
- Village Of Mifflin WwtpMifflin · 0.9 mi away · NPDES OH0146501Recent violation
- Mwcd - Johnny Appleseed WwtpAshland · 2.1 mi away · NPDES OH0130443Recent violation
- Village Of Lucas WwtpLucas · 4.9 mi away · NPDES OH0021041Recent violation
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: 2021-10-11
Monitoring stations: 3