Summit Lake is a 202-acre highly nutrient-loaded hypereutrophic lake in Union County, Iowa. 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 with 1 public boat landing. Compared to the 5 other monitored lakes in Union County, Summit Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-30. Grade methodology: LakeGrade methodology.
Watch Summit Lake water quality
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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 1.4 ft of visibility. Chlorophyll-a: 45.7 µg/L. Trophic State Index: 70.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.4 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 45.7 µg/L | F |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 202 acres |
| Public Access | Yes |
Where to stay near Summit Lake
Compare lakeside cabins, hotels, and vacation rentals near Summit Lake in Union 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.
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Fishing Summit Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.042 m/yr | 5 |
| Chlorophyll-a | ↑ Improving | -5.66 µg/L/yr | 5 |
Recreation & Access
Water Temperature
Summit Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 80°F) and coldest in Sep (about 70°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 26 field readings (2010–2023) via the EPA Water Quality Portal. See the full Summit Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Summit Lake, reaching a maximum surveyed depth of 10 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #5 of 6 lakes in Union County
Cleaner Lakes Within 30 Miles
Summit Lake holds Grade F. 3 nearby lakes hold higher grades.
- DThree Mile LakeUnion County · 9.6 mi · Higher grade (F → D)
- DNodaway LakeAdair County · 16.7 mi · Higher grade (F → D)
- DBinder LakeAdams County · 16.8 mi · Higher grade (F → D)
Nearby Lakes in Union County
Explore Summit Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Summit Lake is a man-made reservoir impounded by the Summit Lake Dam (completed 1935), built primarily for recreation on the TR-WEST PLATTE RIVER; earth-type dam, 26 ft tall and 1,000 ft long.
- Surface area
- 202 ac
- Normal storage
- 1,410 ac-ft
- Max storage
- 2,680 ac-ft
- Drainage area
- 15.7 sq mi
- Hazard class
- Low
- Owner
- Creston Waterworks
Source: USACE National Inventory of Dams, NID ID IA01379 · Operator website
EPA Impairment Status
Summit 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 05-PLA-1470 · Official waterbody report · Matched by proximity (1.17 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Summit Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Cromwell, City-Stp -SirwaCromwell · 3.5 mi away · NPDES IA0074063Recent violation
- Creston City Water Treatment PlantCreston · 0.1 mi away · NPDES IA0078514
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)
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: 2024-09-30
Monitoring stations: 1