Hawthorn Lake
Mahaska County, Iowa160 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Hawthorn Lake. Here is what has been measured.
- Eutrophic
- Impaired · Algal growth
- 29 ft max depth
- Public access
Hawthorn Lake in Mahaska County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 2.4 ft visibility. Phosphorus: 60 µg/L. Chlorophyll-a (algae): 27.5 µg/L. Surface area: 160 acres.
Free interactive depth-contour map of Hawthorn Lake, reaching a maximum surveyed depth of 28 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Hawthorn Lake is a 160-acre productive, nutrient-rich eutrophic lake in Mahaska County, Iowa with an estimated average depth of about 29 feet. Water clarity is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 2 other monitored lakes in Mahaska County, Hawthorn Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-08-28. Methodology: how these readings are compared.
What Hawthorn Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
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.
Nutrient and algae readings are not a swimming clearance. Hawthorn Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
Whether Hawthorn 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 Hawthorn Lake
These are the measurements Iowa DNR publishes for Hawthorn 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 2.4 ft of visibility. Phosphorus 60 µg/L. Chlorophyll-a 27.5 µg/L. TSI 64.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 60µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 27.5µg/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. | 64 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Hawthorn Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Hawthorn Lake typically sits around 58°F at the surface in October. Summer average is about 79°F. Usually warmest in Jul (about 82°F) and coldest in Apr (about 55°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (55°F) to its warmest (82°F).
Typical surface water temperature by month, from 51 field readings (2011–2023) via the EPA Water Quality Portal. See the full Hawthorn Lake water temperature breakdown →
Lake Details
Max depth
~29 ft est.
Surface area
160 acres
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 Hawthorn Lake.
Lake Size & Watershed
Watershed (drainage) area
3 sq mi
HydroLAKES / HydroSHEDS
Shoreline
5.1 mi
HydroLAKES / HydroSHEDS
Elevation
794 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.
Recreation & Access
- Hawthorn Widlife AreaPublic
- Hawthorn Widlife AreaPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Hawthorn Lake
Compare lakeside cabins, hotels, and vacation rentals near Hawthorn Lake in Mahaska 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 Hawthorn Lake are listed below.
Top-rated places to stay near Hawthorn Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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? Cabins and lodging at Hawthorn Lake → · more Iowa lake trips
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Fishing Hawthorn Lake
Water Quality Trend: Stable
Based on 5 years of monitoring (2020–2024).
Water clarity
Improving5 years
Phosphorus
Worsening+56.6 µg/L/yr4 years
Chlorophyll-a
Stable-0.27 µg/L/yr5 years
Reservoir Info (USACE NID)
Hawthorn Lake is a man-made reservoir impounded by the Hawthorne Lake Dam (completed 1979), built primarily for recreation on the PLEASANT CREEK; earth-type dam, 45 ft tall and 900 ft long.
- Surface area
- 160 ac
- Normal storage
- 1,890 ac-ft
- Max storage
- 4,100 ac-ft
- Drainage area
- 5.2 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA01874 · Operator website · Matched by proximity (0.14 km)
EPA Impairment Status
Hawthorn Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 03-NSK-862 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Hawthorn Lake under Clean Water Act (NPDES) discharge permits.
- Barnes City, City Of StpBarnes City · 2.5 mi away · NPDES IA0081329
- S + S FarmGibson · 4.4 mi away · NPDES IA0077887
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 Mahaska County
Frequently asked questions about Hawthorn Lake
Where is Hawthorn Lake?
- Hawthorn Lake is a lake in Mahaska County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Hawthorn Lake?
- Hawthorn Lake in Mahaska County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 2.4 ft visibility. Phosphorus: 60 µg/L. Chlorophyll-a (algae): 27.5 µg/L. Surface area: 160 acres.
Is Hawthorn Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Hawthorn Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
What is the water temperature of Hawthorn Lake?
- Hawthorn Lake typically sits around 58°F at the surface in October, from 51 EPA Water Quality Portal field readings (2011–2023). That is a typical value for the month, not a live reading.
How deep is Hawthorn Lake?
- No published bathymetric survey covers Hawthorn Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 29 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 160 acres.
Are there boat ramps on Hawthorn Lake?
- Hawthorn Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Hawthorn Widlife Area, Hawthorn Widlife Area. Public access is listed as yes.
Can I fish at Hawthorn Lake?
- Hawthorn Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. 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 Hawthorn Lake across LakeQuality
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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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory