Nelson Lake
Crawford County, Iowa11 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Nelson Lake. Here is what has been measured.
- Hypereutrophic
Nelson Lake in Crawford County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 3.8 ft visibility. Phosphorus: 123.5 µg/L. Chlorophyll-a (algae): 30.6 µg/L. Surface area: 11 acres.
Free interactive depth-contour map of Nelson Lake, reaching a maximum surveyed depth of 22 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Nelson Lake is a 11-acre highly nutrient-loaded hypereutrophic lake in Crawford County, Iowa. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Crawford County, Nelson Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-03. Methodology: how these readings are compared.
Swimming conditions
Readings onlyAlgae risk
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Nelson Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Nelson Lake
These are the measurements Iowa DNR publishes for Nelson Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 3.8 ft. Phosphorus 123.5 µg/L. Chlorophyll-a 30.6 µg/L. TSI 65.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 124µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 30.6µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 65 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Nelson Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Nelson Lake typically sits around 78°F at the surface in August. Summer average is about 78°F. Usually warmest in Jul (about 78°F) and coldest in May (about 63°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (63°F) to its warmest (78°F).
Typical surface water temperature by month, from 29 field readings (2010–2023) via the EPA Water Quality Portal. See the full Nelson Lake water temperature breakdown →
Lake Details
Surface area
11 acres
No bathymetric survey has been published for Nelson Lake, so its depth is not documented here.
Stays via Stay22
Stays near Nelson Lake
Compare lakeside cabins, hotels, and vacation rentals near Nelson Lake in Crawford 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Nelson Lake are listed below.
Top-rated places to stay near Nelson Lake
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Fishing Nelson Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Phosphorus
Worsening+99.95 µg/L/yr4 years
Chlorophyll-a
Worsening+5.45 µg/L/yr5 years
Reservoir Info (USACE NID)
Nelson Lake is a man-made reservoir impounded by the Iowa Noname8 (completed 1964), built primarily for recreation on the TR-BOYER RIVER; earth-type dam, 38 ft tall and 522 ft long.
- Surface area
- 11 ac
- Normal storage
- 111 ac-ft
- Max storage
- 220 ac-ft
- Drainage area
- 0.97 sq mi
- Hazard class
- Low
- Owner
- Crawford County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00233 · Operator website · Matched by proximity (0.08 km)
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Nelson Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Dow City, City Of StpDow City · 4.9 mi away · NPDES IA0034371Recent violation
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.
Nearby Lakes in Crawford County
Frequently asked questions about Nelson Lake
Where is Nelson Lake?
- Nelson Lake is a lake in Crawford County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Nelson Lake?
- Nelson Lake in Crawford County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 3.8 ft visibility. Phosphorus: 123.5 µg/L. Chlorophyll-a (algae): 30.6 µg/L. Surface area: 11 acres.
Is Nelson Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Nelson Lake?
- Nelson Lake typically sits around 78°F at the surface in August, from 29 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Nelson Lake across LakeQuality
More lakes in Iowa
Other Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
62 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_WQX62 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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)