Oldham Lake
Monona County, Iowa16 acresView mapDirections
Nutrients and algae sit mid-range for this region.
- Eutrophic
- #1 of 2 in the county
Oldham Lake in Monona County, Iowa has a water quality grade of C (Fair). Water clarity: 5.1 ft visibility. Phosphorus: 46 µg/L. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 16.1 acres.
- Clarity
- 5.1 ft
- Typical in August
- 77°F
- Area
- 16 acres
- Type
- Eutrophic
- Phosphorus
- 46 µg/L
- Chlorophyll-a
- 8.5 µg/L
- Trend
- ↓ Declining
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Watch Oldham Lake’s letter
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Free interactive depth-contour map of Oldham Lake, reaching a maximum surveyed depth of 18 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Oldham Lake is a 16-acre productive, nutrient-rich eutrophic lake in Monona County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Monona County, Oldham Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-03. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyModerate
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 C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Murky, only visible to about 5.1 ft. Phosphorus 46 µg/L. Chlorophyll-a 8.5 µg/L. TSI 55. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.1 ft | Not graded |
| Phosphorus | 46 µg/L | Fair |
| Chlorophyll-a (Algae) | 8.5 µg/L | Good |
| Trophic State Index (TSI) | 55 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Oldham Lake typically sits around 77°F at the surface in August. Summer average is about 77°F. Usually warmest in Jun (about 77°F) and coldest in May (about 64°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 26 field readings (2010–2023) via the EPA Water Quality Portal. See the full Oldham Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 16 acres |
No bathymetric survey has been published for Oldham Lake, so its depth is not documented here.
Fishing Oldham Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.175 m/yr | 4 |
| Phosphorus | ↓ Declining | +1.35 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | +0.15 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Oldham Lake is a man-made reservoir impounded by the Davis-Battle Cr. Watershed Site D-3 (completed 1963), built primarily for fire protection, stock, or small fish pond on the TR-SOLDIER RIVER; earth-type dam, 46 ft tall and 600 ft long.
- Surface area
- 16.1 ac
- Normal storage
- 194 ac-ft
- Max storage
- 285 ac-ft
- Drainage area
- 1.06 sq mi
- Hazard class
- Low
- Owner
- Monona County SWCD
All listed purposes: Fire Protection, Stock, Or Small Fish Pond;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID IA00771 · Operator website · Matched by proximity (0.08 km)
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Oldham Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Ute City Of StpUte · 4.7 mi away · NPDES IA0043010Recent violation
- Soldier City Of StpSoldier · 1.9 mi away · NPDES IA0061743
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 #1 of 2 lakes in Monona County
Nearby Lakes With Higher Grades
Oldham Lake holds Grade C. 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 Monona County
Frequently asked questions about Oldham Lake
Where is Oldham Lake?
- Oldham Lake is a lake in Monona County, Iowa. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Oldham Lake?
- Oldham Lake in Monona County, Iowa has a water quality grade of C (Fair). Water clarity: 5.1 ft visibility. Phosphorus: 46 µg/L. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 16.1 acres.
Is Oldham Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Oldham Lake?
- Oldham Lake typically sits around 77°F at the surface in August, from 26 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Oldham Lake across LakeQuality
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
54 measurements from 1 monitoring station, 2021–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX54 samples · 2021–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- In-Vitro Determination of Chlorophyll
- ISU modification of APHA 2130-B
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)