Lake Diane
Hillsdale County, Michigan290 acresView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #2 of 2 in the county
- 27 ft max depth
- Public access
Lake Diane in Hillsdale County, Michigan has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 51 µg/L. Chlorophyll-a (algae): 20 µg/L. Surface area: 290 acres.
- Clarity
- 2.5 ft
- Typical in September
- 57°F
- Max depth
- ~27 ft est.
- Area
- 290 acres
- Type
- Eutrophic
- Phosphorus
- 51 µg/L
- Chlorophyll-a
- 20 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
Stays via Stay22
Stays near Lake Diane
Compare lakeside cabins, hotels, and vacation rentals near Lake Diane in Hillsdale County, Michigan — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Lake Diane are listed below.
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Watch Lake Diane’s letter
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Lake Diane is a 290-acre productive, nutrient-rich eutrophic lake in Hillsdale County, Michigan with an estimated average depth of about 27 feet. Water quality is graded D based on 2 sampling years through 2021. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 1 other monitored lakes in Hillsdale County, Lake Diane ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, EGLE, last sampled 2021-09-26. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
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 D is nutrients and algae, not a swimming clearance. Lake Diane is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.5 ft of visibility. Phosphorus 51 µg/L. Chlorophyll-a 20 µg/L. TSI 62. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 51 µg/L | Fair |
| Chlorophyll-a (Algae) | 20 µg/L | Poor |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Lake Diane typically sits around 57°F at the surface in September. Summer average is about 59°F. Usually warmest in Jul (about 60°F) and coldest in May (about 53°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 443 field readings (2011–2017) via the EPA Water Quality Portal. See the full Lake Diane water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~27 ft est. |
| Average Depth | ~9 ft est. |
| Surface Area | 290 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Michigan has not published bathymetry for Lake Diane.
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 Lake Diane
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.057 m/yr | 4 |
| Phosphorus | ↓ Declining | +5.04 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +4.89 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Lake Diane is a man-made reservoir impounded by the Lake Diane Dam (completed 1966), built primarily for recreation on the Tributary to Clark Fork Creek; earth-type dam, 19 ft tall and 190 ft long.
- Surface area
- 290 ac
- Normal storage
- 1,700 ac-ft
- Max storage
- 3,200 ac-ft
- Drainage area
- 4.3 sq mi
- Hazard class
- Significant
- Owner
- Hillsdale County Drain Commissioner
Source: USACE National Inventory of Dams, NID ID MI00416 · Operator website · Matched by proximity (0.71 km)
EPA Impairment Status
Lake Diane 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 MI041000030106-01 · Official waterbody report · Matched by proximity (0.92 km)
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Lake Diane under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Pioneer Boy Scout CampPioneer · 1.7 mi away · NPDES OH0146421Recent violation
- Aqua Ohio Lake Seneca WtpMontpelier · 2.3 mi away · NPDES OH0138631Recent violation
- Mdot-M99-Hillsdale ReconstructHillsdale · 3.2 mi away · NPDES MIG081063
- Mdot-M99-HillsdaleHillsdale · 3.2 mi away · NPDES MIG081090
- Nettle Lake Area StpMontpelier · 3.9 mi away · NPDES OH0053376
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.
County Ranking
Ranked #2 of 2 lakes in Hillsdale County
Nearby Lakes With Higher Grades
Lake Diane holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Hillsdale County
Frequently asked questions about Lake Diane
Where is Lake Diane?
- Lake Diane is a lake in Hillsdale County, Michigan. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Diane?
- Lake Diane in Hillsdale County, Michigan has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 51 µg/L. Chlorophyll-a (algae): 20 µg/L. Surface area: 290 acres.
Is Lake Diane safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Lake Diane is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Lake Diane?
- Lake Diane typically sits around 57°F at the surface in September, from 443 EPA Water Quality Portal field readings (2011–2017). That is a typical value for the month, not a live reading.
How deep is Lake Diane?
- No published bathymetric survey covers Lake Diane, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 27 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 290 acres.
Explore Lake Diane across LakeQuality
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Where this data comes from
66 measurements from 1 monitoring station, 2016–2021. Retrieved from the EPA Water Quality Portal on 2026-08-26.
Collected and reported by
- Michigan EGLE - MiCorps
21MICH_MICORPS66 samples · 2016–2021
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (1)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)