Browns Lake is a highly nutrient-loaded hypereutrophic lake in Woodbury County, Iowa. Water quality is graded F 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 1 public boat landing. Compared to the 2 other monitored lakes in Woodbury County, Browns Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-03. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Browns Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 8 samples across 2 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Iowa’s current beach and health-department advisories before swimming.
Water Quality Grade: F, Very Poor
Very murky, less than 0.6 ft of visibility. Chlorophyll-a: 61.6 µg/L. Trophic State Index: 78.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 0.6 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 61.6 µg/L | F |
| Trophic State Index (TSI) | 78 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Browns Lake
Compare lakeside cabins, hotels, and vacation rentals near Browns Lake in Woodbury 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.
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Fishing Browns Lake
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.034 m/yr | 4 |
| Chlorophyll-a | ↑ Improving | -14.17 µg/L/yr | 4 |
Recreation & Access
Water Temperature
Browns Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 80°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 31 field readings (2010–2023) via the EPA Water Quality Portal. See the full Browns Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Browns Lake, reaching a maximum surveyed depth of 10 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #3 of 3 lakes in Woodbury County
Cleaner Lakes Within 30 Miles
Browns Lake holds Grade F. 2 nearby lakes hold higher grades.
- CLittle Sioux Park LakeWoodbury County · 28.3 mi · Two grade letters higher (F → C)
- DSnyder Bend LakeWoodbury County · 1.9 mi · Higher grade (F → D)
Nearby Lakes in Woodbury County
Explore Browns Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
More records, surveys & data sources
EPA Impairment Status
Browns 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-WEM-1735 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Browns Lake under Clean Water Act (NPDES) discharge permits, including 3 classified by the EPA as major dischargers. 3 facilities have a reported Clean Water Act violation in the past three years.
- Midamerican Energy - Neal North Energy CenterSergeant Bluff · 2.7 mi away · NPDES IA0004103MajorRecent violation
- Gelita Usa, Inc.Sergeant Bluff · 3.2 mi away · NPDES IA0004413MajorRecent violation
- Cf Industries Nitrogen, Llc - Port Neal Nitrogen ComplexSergeant Bluff · 3.2 mi away · NPDES IA0004014Major
- Ag Processing Inc. - Sergeant BluffSergeant Bluff · 1.7 mi away · NPDES IA0058815Recent violation
- Salix City Of StpSalix · 2.2 mi away · NPDES IA0032913
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2024-09-03
Monitoring stations: 1