Lake Minnewashta
Dickinson County, IowaView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from D at the last regrade
- Eutrophic
- #2 of 8 in the county
- Public access
Lake Minnewashta in Dickinson County, Iowa has a water quality grade of C (Fair). Water clarity: 2.8 ft visibility. Phosphorus: 47 µg/L. Chlorophyll-a (algae): 19 µg/L.
- Clarity
- 2.8 ft
- Typical in September
- 72°F
- Type
- Eutrophic
- Phosphorus
- 47 µg/L
- Chlorophyll-a
- 19 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Watch Lake Minnewashta’s letter
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Free interactive depth-contour map of Lake Minnewashta, reaching a maximum surveyed depth of 14 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Lake Minnewashta is a productive, nutrient-rich eutrophic lake in Dickinson County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 7 other monitored lakes in Dickinson County, Lake Minnewashta ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-10. Grade methodology: LakeQuality methodology.
What Lake Minnewashta is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
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 C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Very murky, less than 2.8 ft of visibility. Phosphorus 47 µg/L. Chlorophyll-a 19 µg/L. TSI 60. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.8 ft | Not graded |
| Phosphorus | 47 µg/L | Fair |
| Chlorophyll-a (Algae) | 19 µg/L | Fair |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Lake Minnewashta typically sits around 72°F at the surface in September. Summer average is about 75°F. Usually warmest in Jul (about 80°F) and coldest in Jun (about 70°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 27 field readings (2010–2023) via the EPA Water Quality Portal. See the full Lake Minnewashta water temperature breakdown →
Recreation & Access
- Minnewashta Lake Minnewashta LakePublic
- Oak Hill MarinaSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake Minnewashta
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.068 m/yr | 5 |
| Phosphorus | ↑ Improving | -2.75 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -2.04 µg/L/yr | 5 |
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Lake Minnewashta under Clean Water Act (NPDES) discharge permits.
- Arnolds Park Amusement Park ConstructionArnolds Park · 0.7 mi away · NPDES IA0052813
- Arnolds Park 2019 Promenade Beautification ProjectArnolds Park · 0.8 mi away · NPDES IA0053081
- Calvary United Method Church - Arnolds ParkArnolds Park · 0.9 mi away · NPDES IA0052454
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 8 lakes in Dickinson County
Nearby Lakes With Higher Grades
Lake Minnewashta 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 Dickinson County
Frequently asked questions about Lake Minnewashta
Where is Lake Minnewashta?
- Lake Minnewashta is a lake in Dickinson County, Iowa. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Minnewashta?
- Lake Minnewashta in Dickinson County, Iowa has a water quality grade of C (Fair). Water clarity: 2.8 ft visibility. Phosphorus: 47 µg/L. Chlorophyll-a (algae): 19 µg/L.
Is Lake Minnewashta 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 Lake Minnewashta?
- Lake Minnewashta typically sits around 72°F at the surface in September, from 27 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Are there boat ramps on Lake Minnewashta?
- Lake Minnewashta has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Minnewashta Lake Minnewashta Lake, Oak Hill Marina. Public access is listed as yes.
Explore Lake Minnewashta across LakeQuality
Species activity outlook by water temperature and season
Top lakes and where to stay in the Iowa Great Lakes area
Where to stay at Iowa's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
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More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
57 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_WQX57 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Named boat-access points from the USGS National Boat Ramps inventory