Union Grove Lake
Tama County, Iowa117 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Union Grove Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Algal growth
Union Grove Lake in Tama County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 1.6 ft visibility. Phosphorus: 143.5 µg/L. Chlorophyll-a (algae): 88.5 µg/L. Surface area: 117 acres.
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. 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. Methodology: how these readings are compared.
Union Grove Lake covers about 120 acres in Tama County. Vrbo is where to look for cabins and lake homes around Union Grove Lake, and Booking.com and Expedia search hotels near the lake for your dates.
Swimming conditions
Readings onlyBacteria advisory
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are 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.
Whether Union Grove Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Union Grove Lake
These are the measurements Iowa DNR publishes for Union Grove Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.6 ft of visibility. Phosphorus 143.5 µg/L. Chlorophyll-a 88.5 µg/L. TSI 74.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 144µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 88.5µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 74 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Union Grove Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (67°F) to its warmest (80°F).
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
Surface area
117 acres
No bathymetric survey has been published for Union Grove Lake, so its depth is not documented here.
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 readings cover 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 Oct 16–18, 4 adults. Change dates on the map below.
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Fishing Union Grove Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2020–2024).
Water clarity
Improving5 years
Phosphorus
Improving-61.55 µg/L/yr4 years
Chlorophyll-a
Improving-8.2 µg/L/yr5 years
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
Designated uses not supporting: Aquatic life, Recreation.
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.
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. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Union Grove Lake?
- Union Grove Lake in Tama County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. 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?
- Nutrient and algae readings are 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
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Other 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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)