Willow Lake
Harrison County, Iowa19 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Willow Lake. Here is what has been measured.
- Eutrophic
Willow Lake in Harrison County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 4.8 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 9.5 µg/L. Surface area: 19 acres.
Free interactive depth-contour map of Willow Lake, reaching a maximum surveyed depth of 22 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Willow Lake is a 19-acre productive, nutrient-rich eutrophic lake in Harrison County, Iowa. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Harrison County, Willow Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-03. Methodology: how these readings are compared.
Willow Lake covers about 19 acres in Harrison County. Vrbo is where to look for cabins and lake homes around Willow Lake, and Booking.com and Expedia search hotels near the lake for your dates.
Swimming conditions
Readings onlyBacteria tested: low
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, Willow Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 7 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 Willow 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 Willow Lake
These are the measurements Iowa DNR publishes for Willow 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 4.8 ft. Phosphorus 35 µg/L. Chlorophyll-a 9.5 µg/L. TSI 54.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 35µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 9.5µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 54 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Willow Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Willow Lake typically sits around 79°F at the surface in August. Summer average is about 78°F. Usually warmest in Jul (about 79°F) and coldest in May (about 65°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (65°F) to its warmest (79°F).
Typical surface water temperature by month, from 26 field readings (2010–2023) via the EPA Water Quality Portal. See the full Willow Lake water temperature breakdown →
Lake Details
Surface area
19 acres
No bathymetric survey has been published for Willow Lake, so its depth is not documented here.
Stays via Stay22
Stays near Willow Lake
Compare lakeside cabins, hotels, and vacation rentals near Willow Lake in Harrison 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 Willow Lake
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Fishing Willow Lake
Water Quality Trend: Worsening
Based on 4 years of monitoring (2021–2024).
Water clarity
Worsening4 years
Phosphorus
Worsening+14.75 µg/L/yr4 years
Chlorophyll-a
Worsening+2.09 µg/L/yr4 years
Reservoir Info (USACE NID)
Willow Lake is a man-made reservoir impounded by the Willow Lake Dam (completed 1976), built primarily for debris control on the TR-WILLOW CREEK; earth-type dam, 31 ft tall and 390 ft long.
- Surface area
- 19 ac
- Normal storage
- 21 ac-ft
- Max storage
- 44 ac-ft
- Drainage area
- 0.21 sq mi
- Hazard class
- Low
- Owner
- Harrison County Conservation Board
All listed purposes: Debris Control;Recreation.
Source: USACE National Inventory of Dams, NID ID IA01566 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Willow Lake under Clean Water Act (NPDES) discharge permits.
- Crossroads Cattle CompanyWoodbine · 3.4 mi away · NPDES IA0080667
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 Harrison County
Frequently asked questions about Willow Lake
Where is Willow Lake?
- Willow Lake is a lake in Harrison County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Willow Lake?
- Willow Lake in Harrison County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 4.8 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 9.5 µg/L. Surface area: 19 acres.
Is Willow Lake safe to swim in?
- Based on E. coli testing, Willow Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 7 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 Willow 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 Willow Lake?
- Willow Lake typically sits around 79°F at the surface in August, from 26 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Willow Lake across LakeQuality
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Where this data comes from
54 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_WQX54 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)