Lake Hendricks is a 50-acre highly nutrient-loaded hypereutrophic lake in Howard County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-10-21. Grade methodology: LakeGrade methodology.
Watch Lake Hendricks water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1.5 ft of visibility. Chlorophyll-a: 99.1 µg/L. Trophic State Index: 74.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 99.1 µg/L | F |
| Trophic State Index (TSI) | 74 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 50 acres |
Where to stay near Lake Hendricks
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Fishing Lake Hendricks
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.039 m/yr | 4 |
| Chlorophyll-a | ↓ Declining | +28.29 µg/L/yr | 4 |
Water Temperature
Lake Hendricks averages about 77°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Sep (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 26 field readings (2010–2023) via the EPA Water Quality Portal. See the full Lake Hendricks water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Lake Hendricks, reaching a maximum surveyed depth of 14 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #1 of 1 lakes in Howard County
Cleaner Lakes Within 30 Miles
Lake Hendricks holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Howard County
Explore Lake Hendricks across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Bremer County · Clarity: 1.2 ft
Winneshiek County · Clarity: 3.1 ft
Cerro Gordo County · Clarity: 2.3 ft
Black Hawk County · Clarity: 1.9 ft
Black Hawk County · Clarity: 1.6 ft
Black Hawk County · Clarity: 1.6 ft
Hypereutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Lake Hendricks is a man-made reservoir impounded by the Lake Hendricks Dam (completed 1960), built primarily for recreation on the TR-WAPSIPINICON RIVER; earth-type dam, 30 ft tall and 2,375 ft long.
- Surface area
- 50 ac
- Normal storage
- 500 ac-ft
- Max storage
- 960 ac-ft
- Drainage area
- 1.88 sq mi
- Hazard class
- Significant
- Owner
- Howard County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00495 · Operator website
EPA Impairment Status
Lake Hendricks 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 01-WPS-356 · Official waterbody report
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 Lake Hendricks under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Riceville City Of StpRiceville · 1.2 mi away · NPDES IA0032514Recent 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
Most recent sample: 2024-10-21
Monitoring stations: 1