Blue Lake
Monona County, IowaView mapDirections
Iowa DNR publishes the water-quality measurements for Blue Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Turbidity
- 38 ft max depth
- Public access
Blue Lake in Monona County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 0.9 ft visibility. Phosphorus: 194.5 µg/L. Chlorophyll-a (algae): 37 µg/L.
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.
Blue Lake is a highly nutrient-loaded hypereutrophic lake in Monona County, Iowa with an estimated average depth of about 38 feet. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available. 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. Methodology: how these readings are compared.
Vrbo is where to look for cabins and lake homes around Blue Lake, and Booking.com and Expedia search hotels near the lake for your dates.
Swimming conditions
Readings onlyRecreation use not supported
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.
Based on E. coli testing, Blue Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 5 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.
Whether Blue 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 Blue Lake
These are the measurements Iowa DNR publishes for Blue Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 0.9 ft of visibility. Phosphorus 194.5 µg/L. Chlorophyll-a 37 µg/L. TSI 75.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 0.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 195µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 37µg/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. | 75 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Blue Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Blue Lake typically sits around 80°F at the surface in August. Summer average is about 80°F. Usually warmest in Jul (about 83°F) and coldest in May (about 68°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (68°F) to its warmest (83°F).
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 →
Lake Details
Max depth
~38 ft est.
Public access
Yes
Listed by Iowa DNR
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Blue Lake.
Lake Size & Watershed
Watershed (drainage) area
2 sq mi
HydroLAKES / HydroSHEDS
Surface area
62 acres
HydroLAKES / HydroSHEDS
Shoreline
2 mi
HydroLAKES / HydroSHEDS
Elevation
1,037 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Stays via Stay22
Stays 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Blue Lake are listed below.
Top-rated places to stay near Blue Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Blue Lake
Water Quality Trend: Worsening
Based on 4 years of monitoring (2021–2024).
Water clarity
Worsening4 years
Phosphorus
Worsening+79.65 µg/L/yr4 years
Chlorophyll-a
Worsening+48.51 µg/L/yr4 years
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
Designated uses not supporting: Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 06-WEM-1728 · Official waterbody report
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.
Nearby Lakes in Monona County
Frequently asked questions about Blue Lake
Where is Blue Lake?
- Blue Lake is a lake in Monona County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Blue Lake?
- Blue Lake in Monona County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 0.9 ft visibility. Phosphorus: 194.5 µg/L. Chlorophyll-a (algae): 37 µg/L.
Is Blue Lake safe to swim in?
- Based on E. coli testing, Blue Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 5 samples across 2 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Blue Lake is safe to swim in today is a call for Iowa's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Blue Lake?
- Blue Lake typically sits around 80°F at the surface in August, from 96 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Blue Lake?
- No published bathymetric survey covers Blue Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 38 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Can I fish at Blue Lake?
- Public access to Blue Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Iowa's fish and wildlife agency, so check its current regulations before you go.
Explore Blue Lake across LakeQuality
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Where this data comes from
48 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_WQX48 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)
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)