Grays Lake is a productive, nutrient-rich eutrophic lake in Polk County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 11 other monitored lakes in Polk County, Grays Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-18. Grade methodology: LakeGrade methodology.
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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 1.6 ft of visibility. Chlorophyll-a: 46.5 µg/L. Trophic State Index: 69.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 46.5 µg/L | F |
| Trophic State Index (TSI) | 69 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Grays Lake
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Fishing Grays Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.112 m/yr | 5 |
| Chlorophyll-a | ↓ Declining | +22.9 µg/L/yr | 5 |
Recreation & Access
Water Temperature
Grays Lake averages about 79°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in Sep (about 73°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 16 field readings (2018–2026) via the EPA Water Quality Portal. See the full Grays Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Grays Lake, reaching a maximum surveyed depth of 12 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #6 of 12 lakes in Polk County
Cleaner Lakes Within 30 Miles
Grays Lake holds Grade F. 5 nearby lakes hold higher grades.
- ATerra Park LakePolk County · 7.2 mi · Two grade letters higher (F → A)
- BDale Maffitt ReservoirDallas County · 8.7 mi · Two grade letters higher (F → B)
- CLake PetockaPolk County · 13.9 mi · Two grade letters higher (F → C)
- DThomas Mitchell LakePolk County · 14.2 mi · Higher grade (F → D)
- DEaster LakePolk County · 4.6 mi · Higher grade (F → D)
Nearby Lakes in Polk County
Explore Grays Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
EPA Impairment Status
Grays Lake 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 04-RAC-1118 · Official waterbody report
Regulated Pollution Sources Nearby
10 EPA-permitted facilities operate within about 5 miles of Grays Lake under Clean Water Act (NPDES) discharge permits. 6 facilities have a reported Clean Water Act violation in the past three years.
- Des Moines Tce Superfund SiteDes Moines · 0.7 mi away · NPDES IA0069671Recent violation
- Iowa Methodist Medical CenterDes Moines · 1.3 mi away · NPDES IA0052446Recent violation
- Bituminous Materials And Supply, LpDes Moines · 2.2 mi away · NPDES IA0073172Recent violation
- Mercyone Des Moines Medical CenterDes Moines · 2.2 mi away · NPDES IA0081477Recent violation
- Iowa Lutheran HospitalDes Moines · 2.7 mi away · NPDES IA0052438Recent violation
- Archer Daniels Midland CompanyDes Moines · 4.9 mi away · NPDES IA0072958Recent 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)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2024-09-18
Monitoring stations: 1