Slipbluff Lake
Decatur County, Iowa18 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Mesotrophic
- #2 of 3 in the county
Slipbluff Lake in Decatur County, Iowa has a water quality grade of A (Excellent). Water clarity: 9 ft visibility. Phosphorus: 17.5 µg/L. Chlorophyll-a (algae): 4.5 µg/L. Surface area: 18 acres.
- Clarity
- 9 ft
- Typical in September
- 78°F
- Area
- 18 acres
- Type
- Mesotrophic
- Phosphorus
- 17.5 µg/L
- Chlorophyll-a
- 4.5 µg/L
- Trend
- ↓ Declining
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Watch Slipbluff Lake’s letter
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Free interactive depth-contour map of Slipbluff Lake, reaching a maximum surveyed depth of 21 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Slipbluff Lake is a 18-acre mesotrophic lake in Decatur County, Iowa. Water quality is graded A based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 2 other monitored lakes in Decatur County, Slipbluff Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-15. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLow algae
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 A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 9 ft. Phosphorus 17.5 µg/L. Chlorophyll-a 4.5 µg/L. TSI 45. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9 ft | Not graded |
| Phosphorus | 17.5 µg/L | Good |
| Chlorophyll-a (Algae) | 4.5 µg/L | Good |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Water Temperature
Slipbluff Lake typically sits around 78°F at the surface in September. Summer average is about 79°F. Usually warmest in Jul (about 83°F) and coldest in May (about 71°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 Slipbluff Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 18 acres |
No bathymetric survey has been published for Slipbluff Lake, so its depth is not documented here.
Fishing Slipbluff Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.433 m/yr | 4 |
| Phosphorus | ↓ Declining | +6 µg/L/yr | 4 |
| Chlorophyll-a | ↓ Declining | +0.25 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Slipbluff Lake is a man-made reservoir impounded by the Slip Bluff Park Dam (completed 1970), built primarily for recreation on the TR-POTTEROFF CREEK; earth-type dam, 33 ft tall and 333 ft long.
- Surface area
- 18 ac
- Normal storage
- 230 ac-ft
- Max storage
- 464 ac-ft
- Drainage area
- 0.44 sq mi
- Hazard class
- Low
- Owner
- Decatur County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00349 · Operator website · Matched by proximity (1 km)
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Slipbluff Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Davis City, City Of Stp (Sirwa)Davis City · 2.9 mi away · NPDES IA0060232Recent violation
- Iowa Dot Rest Area #34 I35 LamoniLamoni · 0.2 mi away · NPDES IA0068934
- Procom, Inc.Lamoni · 2.2 mi away · NPDES IA0068144
- Chief Lamoni Motel-StpLamoni · 3.1 mi away · NPDES IA0069051
- Lamoni Industrial Park StpLamoni · 3.4 mi away · NPDES IA0070963
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 3 lakes in Decatur County
Nearby Lakes in Decatur County
Frequently asked questions about Slipbluff Lake
Where is Slipbluff Lake?
- Slipbluff Lake is a lake in Decatur County, Iowa. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Slipbluff Lake?
- Slipbluff Lake in Decatur County, Iowa has a water quality grade of A (Excellent). Water clarity: 9 ft visibility. Phosphorus: 17.5 µg/L. Chlorophyll-a (algae): 4.5 µg/L. Surface area: 18 acres.
Is Slipbluff Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Slipbluff Lake?
- Slipbluff Lake typically sits around 78°F at the surface in September, from 26 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Slipbluff Lake across LakeQuality
More Iowa Lake Rankings
Other Grade A Lakes in Iowa
Mesotrophic 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)