Mormon Trail Lake is a 33-acre productive, nutrient-rich eutrophic lake in Adair County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Compared to the 4 other monitored lakes in Adair County, Mormon Trail Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-29. Grade methodology: LakeGrade methodology.
Watch Mormon Trail Lake water quality
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Swimming Safety
Based on E. coli testing, Mormon Trail Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 8 samples across 3 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: C, Fair
Murky, only visible to about 6.2 ft. Chlorophyll-a: 9.7 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.2 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 9.7 µg/L | B |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 33 acres |
Where to stay near Mormon Trail Lake
Compare lakeside cabins, hotels, and vacation rentals near Mormon Trail Lake in Adair 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 Mormon Trail Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.204 m/yr | 5 |
| Chlorophyll-a | ↑ Improving | -1.14 µg/L/yr | 5 |
Water Temperature
Mormon Trail Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in Sep (about 71°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 Mormon Trail Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Mormon Trail Lake, reaching a maximum surveyed depth of 30 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #1 of 5 lakes in Adair County
Nearby Lakes in Adair County
Explore Mormon Trail Lake across LakeGrade
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Mormon Trail Lake is a man-made reservoir impounded by the Mormon Trail Lake Dam (completed 1965), built primarily for recreation on the TR-WEST FORK NODAWAY; earth-type dam, 46 ft tall and 928 ft long.
- Surface area
- 33 ac
- Normal storage
- 394 ac-ft
- Max storage
- 585 ac-ft
- Drainage area
- 0.65 sq mi
- Hazard class
- Low
- Owner
- Adair County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00021 · Operator website
EPA Impairment Status
Mormon Trail 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-NOD-1404 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mormon Trail Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Bridgewater City Of (Sirwa)Bridgewater · 1.2 mi away · NPDES IA0062006Recent 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.
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
Most recent sample: 2024-09-29
Monitoring stations: 1