Union Grove Lake
Tama County, Iowa117 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Algal growth
- #2 of 3 in the county
Union Grove Lake in Tama County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 143.5 µg/L. Chlorophyll-a (algae): 88.5 µg/L. Surface area: 117 acres.
- Clarity
- 1.6 ft
- Typical in September
- 67°F
- Area
- 117 acres
- Type
- Hypereutrophic
- Phosphorus
- 143.5 µg/L
- Chlorophyll-a
- 88.5 µg/L
- Trend
- ↑ Improving
Stays via Stay22
Stays near Union Grove Lake
Compare lakeside cabins, hotels, and vacation rentals near Union Grove Lake in Tama 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 Union Grove Lake are listed below.
Top-rated places to stay near Union Grove Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Watch Union Grove Lake’s letter
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Free interactive depth-contour map of Union Grove Lake, reaching a maximum surveyed depth of 12 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Union Grove Lake is a 117-acre highly nutrient-loaded hypereutrophic lake in Tama County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Compared to the 2 other monitored lakes in Tama County, Union Grove Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-08-27. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyBacteria advisory
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. Union Grove Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, pathogens (E. coli, fecal), pH / acidity, turbidity. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.6 ft of visibility. Phosphorus 143.5 µg/L. Chlorophyll-a 88.5 µg/L. TSI 74. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 143.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 88.5 µg/L | Poor |
| Trophic State Index (TSI) | 74 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Union Grove Lake typically sits around 67°F at the surface in September. Summer average is about 77°F. Usually warmest in Jul (about 80°F) and coldest in Sep (about 67°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 110 field readings (2010–2023) via the EPA Water Quality Portal. See the full Union Grove Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 117 acres |
No bathymetric survey has been published for Union Grove Lake, so its depth is not documented here.
Fishing Union Grove Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.077 m/yr | 5 |
| Phosphorus | ↑ Improving | -61.55 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -8.2 µg/L/yr | 5 |
Reservoir Info (USACE NID)
Union Grove Lake is a man-made reservoir impounded by the Union Grove Lake Dam (completed 1920), built primarily for recreation on the DEER CREEK; earth-type dam, 29 ft tall and 1,205 ft long.
- Surface area
- 117 ac
- Normal storage
- 770 ac-ft
- Max storage
- 2,120 ac-ft
- Drainage area
- 11 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA01373 · Operator website
EPA Impairment Status
Union Grove 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 02-IOW-724 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Union Grove Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Garwin City Of StpGarwin · 3.6 mi away · NPDES IA0025925Recent violation
- Gladbrook City Of StpGladbrook · 4.4 mi away · NPDES IA0025330Recent 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.
County Ranking
Ranked #2 of 3 lakes in Tama County
Nearby Lakes With Higher Grades
Union Grove Lake holds Grade F. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Tama County
Frequently asked questions about Union Grove Lake
Where is Union Grove Lake?
- Union Grove Lake is a lake in Tama County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Union Grove Lake?
- Union Grove Lake in Tama County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 143.5 µg/L. Chlorophyll-a (algae): 88.5 µg/L. Surface area: 117 acres.
Is Union Grove Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Union Grove Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, pathogens (E. coli, fecal), pH / acidity, turbidity. Check local advisories before you swim.
What is the water temperature of Union Grove Lake?
- Union Grove Lake typically sits around 67°F at the surface in September, from 110 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Union Grove Lake across LakeQuality
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
62 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_WQX62 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)