Blue Lake is a highly nutrient-loaded hypereutrophic lake in Monona County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 1 other monitored lakes in Monona County, Blue Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-19. Grade methodology: LakeGrade methodology.
Watch Blue Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Based on E. coli testing, Blue Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 10.9% of 110 samples across 7 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 0.9 ft of visibility. Chlorophyll-a: 37 µg/L. Trophic State Index: 73.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 0.9 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 37 µg/L | F |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Blue Lake
Compare lakeside cabins, hotels, and vacation rentals near Blue Lake in Monona 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.
Top-rated places to stay near Blue Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to Blue Lake?
Get lake water-quality report cards plus the best cabin & lodging deals near Blue Lake — straight to your inbox. No spam, unsubscribe anytime.
Planning a whole trip? See where to stay at Iowa’s top lakes →
Fishing Blue Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.122 m/yr | 4 |
| Chlorophyll-a | ↓ Declining | +48.51 µg/L/yr | 4 |
Recreation & Access
Water Temperature
Blue Lake averages about 80°F at the surface in summer, usually warmest in Jul (about 83°F) and coldest in May (about 68°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 96 field readings (2010–2023) via the EPA Water Quality Portal. See the full Blue Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Blue 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 #2 of 2 lakes in Monona County
Cleaner Lakes Within 30 Miles
Blue Lake holds Grade F. 3 nearby lakes hold higher grades.
- COldham LakeMonona County · 19.1 mi · Two grade letters higher (F → C)
- CWillow LakeHarrison County · 26.9 mi · Two grade letters higher (F → C)
- DSnyder Bend LakeWoodbury County · 18.7 mi · Higher grade (F → D)
Nearby Lakes in Monona County
Explore Blue 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
Blue Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 06-WEM-1728 · Official waterbody report · Matched by proximity (1.31 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Blue Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Onawa City Of StpOnawa · 4.1 mi away · NPDES IA0036145Recent 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.
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: 2024-09-19
Monitoring stations: 1