Rock Creek Beach Lake is a 640-acre highly nutrient-loaded hypereutrophic lake in Jasper County, Iowa. Water quality is graded F based on 1 sampling years through 2023. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 7 other monitored lakes in Jasper County, Rock Creek Beach Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2023-09-20. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Rock Creek Beach Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.5% of 106 samples across 7 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 1.1 ft of visibility. Trophic State Index: 75.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.1 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 75 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 640 acres |
| Public Access | Yes |
Where to stay near Rock Creek Beach Lake
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Fishing Rock Creek Beach Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.011 m/yr | 5 |
| Chlorophyll-a | ↑ Improving | -2.11 µg/L/yr | 5 |
Recreation & Access
Water Temperature
Rock Creek Beach Lake averages about 79°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in May (about 68°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 79 field readings (2010–2022) via the EPA Water Quality Portal. See the full Rock Creek Beach Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Rock Creek Beach Lake, reaching a maximum surveyed depth of 16 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #5 of 8 lakes in Jasper County
Cleaner Lakes Within 30 Miles
Rock Creek Beach Lake holds Grade F. One nearby lake has a higher grade.
Nearby Lakes in Jasper County
Explore Rock Creek Beach Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Compare Rock Creek Beach Lake With Nearby Lakes
More records, surveys & data sources
Reservoir Info (USACE NID)
Rock Creek Beach Lake is a man-made reservoir impounded by the Rock Creek Dam, built primarily for recreation on the ROCK CREEK; earth-type dam, 33 ft tall and 1,500 ft long.
- Surface area
- 640 ac
- Normal storage
- 5,500 ac-ft
- Max storage
- 13,700 ac-ft
- Drainage area
- 41.4 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA00537 · Operator website · Matched by proximity (0.53 km)
EPA Impairment Status
Rock Creek Beach Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 03-NSK-865 · Official waterbody report · Matched by proximity (1.34 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
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: 2023-09-20
Monitoring stations: 1