Little River Lake is a 787-acre productive, nutrient-rich eutrophic lake in Decatur County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 4 public boat landings. Compared to the 2 other monitored lakes in Decatur County, Little River Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-30. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Little River Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 16.7% of 6 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.
Water Quality Grade: F, Very Poor
Very murky, less than 2.3 ft of visibility. Chlorophyll-a: 70 µg/L. Trophic State Index: 69.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 70 µg/L | F |
| Trophic State Index (TSI) | 69 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 787 acres |
| Public Access | Yes |
Where to stay near Little River Lake
Compare lakeside cabins, hotels, and vacation rentals near Little River Lake in Decatur 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.
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Fishing Little River Lake
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.064 m/yr | 4 |
| Chlorophyll-a | ↑ Improving | -6.34 µg/L/yr | 4 |
Recreation & Access
Water Temperature
Little River Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 79°F) and coldest in May (about 65°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 31 field readings (2010–2023) via the EPA Water Quality Portal. See the full Little River Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Little River Lake, reaching a maximum surveyed depth of 32 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #3 of 3 lakes in Decatur County
Cleaner Lakes Within 30 Miles
Little River Lake holds Grade F. 4 nearby lakes hold higher grades.
- ANine Eagles LakeDecatur County · 10.6 mi · Two grade letters higher (F → A)
- BSlipbluff LakeDecatur County · 7.7 mi · Two grade letters higher (F → B)
- DBob White LakeWayne County · 19.9 mi · Higher grade (F → D)
- DWest Lake OsceolaClarke County · 20.1 mi · Higher grade (F → D)
Nearby Lakes in Decatur County
Explore Little River Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Little River Lake is a man-made reservoir impounded by the Little River Watershed Site M-1 (completed 1984), built primarily for flood risk reduction on the LITTLE RIVER; earth-type dam, 61 ft tall and 1,810 ft long.
- Surface area
- 787 ac
- Normal storage
- 10,869 ac-ft
- Max storage
- 32,650 ac-ft
- Drainage area
- 20.85 sq mi
- Hazard class
- High
- Owner
- Decatur County SWCD
All listed purposes: Flood Risk Reduction;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IA02263 · Operator website · Matched by proximity (0.25 km)
EPA Impairment Status
Little River Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 05-GRA-1358 · Official waterbody report · Matched by proximity (2.91 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Little River Lake under Clean Water Act (NPDES) discharge permits. 3 facilities have a reported Clean Water Act violation in the past three years.
- Leon Water Treatment PlantLeon · 0.5 mi away · NPDES IA0081787Recent violation
- Leon City Of StpLeon · 2.4 mi away · NPDES IA0027871Recent violation
- Decatur City-Stp-SirwaDecatur · 2.7 mi away · NPDES IA0072745Recent 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: 2024-09-30
Monitoring stations: 1