Manteno Lake
Shelby County, Iowa4 acresView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- Impaired · Oxygen depletion (low DO)
- #1 of 6 in the county
Manteno Lake in Shelby County, Iowa has a water quality grade of D (Nutrient-rich). Water clarity: 2.7 ft visibility. Phosphorus: 138.5 µg/L. Chlorophyll-a (algae): 28.3 µg/L. Surface area: 4.4 acres.
- Clarity
- 2.7 ft
- Typical in August
- 77°F
- Area
- 4 acres
- Type
- Eutrophic
- Trend
- → Stable
Stays via Stay22
Stays near Manteno Lake
Compare lakeside cabins, hotels, and vacation rentals near Manteno Lake in Shelby County, Iowa — 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 Manteno Lake are listed below.
Top-rated places to stay near Manteno Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Watch Manteno Lake’s letter
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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.
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. Water clarity 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: 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. Manteno Lake is listed impaired under Clean Water Act §303(d) (IR 5) for oxygen depletion (low DO). Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.7 ft of visibility. Phosphorus 138.5 µg/L. Chlorophyll-a 28.3 µg/L. TSI 67. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.7 ft | Not graded |
| Phosphorus | 138.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 28.3 µg/L | Poor |
| Trophic State Index (TSI) | 67 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Manteno Lake typically sits around 77°F at the surface in August. Summer average is about 76°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 4 acres |
No bathymetric survey has been published for Manteno Lake, so its depth is not documented here.
Fishing Manteno Lake
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.039 m/yr | 5 |
| Phosphorus | ↓ Declining | +23.35 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | -0.69 µg/L/yr | 5 |
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)
County Ranking
Ranked #1 of 6 lakes in Shelby County
Nearby Lakes With Higher Grades
Manteno Lake holds Grade D. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Shelby County
Frequently asked questions about Manteno Lake
Where is Manteno Lake?
- Manteno Lake is a lake in Shelby County, Iowa. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Manteno Lake?
- Manteno Lake in Shelby County, Iowa has a water quality grade of D (Nutrient-rich). Water clarity: 2.7 ft visibility. Phosphorus: 138.5 µg/L. Chlorophyll-a (algae): 28.3 µg/L. Surface area: 4.4 acres.
Is Manteno Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Manteno Lake is listed impaired under Clean Water Act §303(d) (IR 5) for oxygen depletion (low DO). Check local advisories before you swim.
What is the water temperature of Manteno Lake?
- Manteno Lake typically sits around 77°F at the surface in August, from 28 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Manteno Lake across LakeQuality
More Iowa Lake Rankings
Other Grade D Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
49 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX49 samples · 2020–2024
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
Impairment status from EPA ATTAINS 303(d) database