Manteno Lake is a 4-acre productive, nutrient-rich eutrophic lake in Shelby County, Iowa. Water quality is graded D based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Compared to the 5 other monitored lakes in Shelby County, Manteno 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 Manteno Lake water quality
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 2.7 ft of visibility. Chlorophyll-a: 28.3 µg/L. Trophic State Index: 63.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.7 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 28.3 µg/L | D |
| Trophic State Index (TSI) | 63 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 4 acres |
Where to stay near Manteno Lake
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Fishing Manteno Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.039 m/yr | 5 |
| Chlorophyll-a | → Stable | -0.69 µg/L/yr | 5 |
Water Temperature
Manteno Lake averages about 76°F at the surface in summer, usually warmest in Jul (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 28 field readings (2010–2023) via the EPA Water Quality Portal. See the full Manteno Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Manteno Lake, reaching a maximum surveyed depth of 8 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #1 of 6 lakes in Shelby County
Cleaner Lakes Within 30 Miles
Manteno Lake holds Grade D. 2 nearby lakes hold higher grades.
- CWillow LakeHarrison County · 17.5 mi · Higher grade (D → C)
- COldham LakeMonona County · 19.7 mi · Higher grade (D → C)
Nearby Lakes in Shelby County
Explore Manteno Lake across LakeGrade
More Iowa Lake Rankings
Other Grade D Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Manteno Lake is a man-made reservoir impounded by the Mill Picayune Watershed Site M-24-10 (completed 1964), built primarily for fire protection, stock, or small fish pond on the MILL CREEK; earth-type dam, 36 ft tall and 787 ft long.
- Surface area
- 4.4 ac
- Normal storage
- 30 ac-ft
- Max storage
- 166 ac-ft
- Drainage area
- 3.8 sq mi
- Hazard class
- Low
- Owner
- Shelby County SWCD
All listed purposes: Fire Protection, Stock, Or Small Fish Pond;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID IA00992 · Operator website · Matched by proximity (0.06 km)
EPA Impairment Status
Manteno Lake 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 IA 06-BOY-1505 · Official waterbody report · Matched by proximity (0.28 km)
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-03
Monitoring stations: 1