Roberts Creek Lake
Marion County, Iowa296 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Turbidity
- #1 of 1 in the county
- 46 ft max depth
- Public access
Roberts Creek Lake in Marion County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.5 ft visibility. Phosphorus: 115 µg/L. Chlorophyll-a (algae): 44.6 µg/L. Surface area: 296 acres.
- Clarity
- 1.5 ft
- Typical in September
- 69°F
- Max depth
- ~46 ft est.
- Area
- 296 acres
- Type
- Hypereutrophic
- Phosphorus
- 115 µg/L
- Chlorophyll-a
- 44.6 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Roberts Creek Lake
Compare lakeside cabins, hotels, and vacation rentals near Roberts Creek Lake in Marion 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 grade measures nutrients and algae, not lodging — cabins and rentals around Roberts Creek Lake are listed below.
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Free interactive depth-contour map of Roberts Creek Lake, reaching a maximum surveyed depth of 20 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Roberts Creek Lake is a 296-acre highly nutrient-loaded hypereutrophic lake in Marion County, Iowa with an estimated average depth of about 46 feet. 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.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-17. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The F is nutrients and algae, not a swimming clearance. Roberts Creek Lake is listed impaired under Clean Water Act §303(d) (IR 5) for turbidity. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.5 ft of visibility. Phosphorus 115 µg/L. Chlorophyll-a 44.6 µg/L. TSI 71. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | Not graded |
| Phosphorus | 115 µg/L | Poor |
| Chlorophyll-a (Algae) | 44.6 µg/L | Poor |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Roberts Creek Lake typically sits around 69°F at the surface in September. Summer average is about 78°F. Usually warmest in Jul (about 80°F) and coldest in Sep (about 69°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 29 field readings (2010–2023) via the EPA Water Quality Portal. See the full Roberts Creek Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~46 ft est. |
| Average Depth | ~17 ft est. |
| Surface Area | 296 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Roberts Creek Lake.
Lake Size & Watershed
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.
Fishing Roberts Creek Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.036 m/yr | 5 |
| Phosphorus | ↓ Declining | +14 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -11.27 µg/L/yr | 5 |
Reservoir Info (USACE NID)
Roberts Creek Lake is a man-made reservoir impounded by the Roberts Creek Dam (completed 1968), built primarily for recreation on the Roberts Creek; earth-type dam, 60 ft tall and 2,400 ft long.
- Surface area
- 296 ac
- Normal storage
- 3,043 ac-ft
- Max storage
- 21,863 ac-ft
- Drainage area
- 13.28 sq mi
- Hazard class
- Significant
- Owner
- Marion County Board of Supervisors
All listed purposes: Recreation;Other.
Source: USACE National Inventory of Dams, NID ID IA00655 · Operator website
EPA Impairment Status
Roberts Creek 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-LDM-1019 · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Roberts Creek Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Park Hills Wastewater FacilityOtley · 1.4 mi away · NPDES IA0075434Recent violation
- Lake Red Rock - Whitebreast Sewage LagoonKnoxville · 3.1 mi away · NPDES IA0083402Recent violation
- Lake Red Rock - North Overlook Sewage LagoonKnoxville · 4.9 mi away · NPDES IA0083399
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.
County Ranking
Ranked #1 of 1 lakes in Marion County
Nearby Lakes With Higher Grades
Roberts Creek Lake holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Marion County
Frequently asked questions about Roberts Creek Lake
Where is Roberts Creek Lake?
- Roberts Creek Lake is a lake in Marion County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Roberts Creek Lake?
- Roberts Creek Lake in Marion County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.5 ft visibility. Phosphorus: 115 µg/L. Chlorophyll-a (algae): 44.6 µg/L. Surface area: 296 acres.
Is Roberts Creek Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Roberts Creek Lake is listed impaired under Clean Water Act §303(d) (IR 5) for turbidity. Check local advisories before you swim.
What is the water temperature of Roberts Creek Lake?
- Roberts Creek Lake typically sits around 69°F at the surface in September, from 29 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Roberts Creek Lake?
- No published bathymetric survey covers Roberts Creek Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 46 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 296 acres.
Explore Roberts Creek Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Iowa's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
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Where this data comes from
60 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_WQX60 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)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated 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)