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: LakeGrade methodology.
Watch Oldham Lake water quality
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 5.1 ft. Chlorophyll-a: 8.5 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.1 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 8.5 µg/L | B |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 16 acres |
Where to stay near Oldham Lake
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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 |
| Chlorophyll-a | → Stable | +0.15 µg/L/yr | 4 |
Water Temperature
Oldham Lake averages about 77°F at the surface in summer, 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 →
Location & Depth Map
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.
County Ranking
Ranked #1 of 2 lakes in Monona County
Nearby Lakes in Monona County
Explore Oldham Lake across LakeGrade
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-03
Monitoring stations: 1