Mormon Trail Lake
Adair County, Iowa33 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Eutrophic
- Impaired · Mercury
- #1 of 5 in the county
- 25 ft max depth
Mormon Trail Lake in Adair County, Iowa has a water quality grade of B (Good). Water clarity: 6.2 ft visibility. Phosphorus: 25 µg/L. Chlorophyll-a (algae): 9.7 µg/L. Surface area: 33 acres.
- Clarity
- 6.2 ft
- Typical in September
- 71°F
- Max depth
- ~25 ft est.
- Area
- 33 acres
- Type
- Eutrophic
- Phosphorus
- 25 µg/L
- Chlorophyll-a
- 9.7 µg/L
- Trend
- ↑ Improving
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Watch Mormon Trail Lake’s letter
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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.
Mormon Trail Lake is a 33-acre productive, nutrient-rich eutrophic lake in Adair County, Iowa with an estimated average depth of about 25 feet. Water quality is graded B 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: LakeQuality methodology.
Swimming Safety
Grade onlyBacteria A
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.
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: B (Good)
Murky, only visible to about 6.2 ft. Phosphorus 25 µg/L. Chlorophyll-a 9.7 µg/L. TSI 51. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.2 ft | Not graded |
| Phosphorus | 25 µg/L | Good |
| Chlorophyll-a (Algae) | 9.7 µg/L | Good |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Mormon Trail Lake typically sits around 71°F at the surface in September. Summer average is about 78°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~25 ft est. |
| Average Depth | ~12 ft est. |
| Surface Area | 33 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Mormon Trail 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 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 |
| Phosphorus | ↓ Declining | +37.2 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -1.14 µg/L/yr | 5 |
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
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.
County Ranking
Ranked #1 of 5 lakes in Adair County
Nearby Lakes in Adair County
Frequently asked questions about Mormon Trail Lake
Where is Mormon Trail Lake?
- Mormon Trail Lake is a lake in Adair County, Iowa. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mormon Trail Lake?
- Mormon Trail Lake in Adair County, Iowa has a water quality grade of B (Good). Water clarity: 6.2 ft visibility. Phosphorus: 25 µg/L. Chlorophyll-a (algae): 9.7 µg/L. Surface area: 33 acres.
Is Mormon Trail Lake safe to swim in?
- 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. That works out to a bacteria swim-safety grade of A — a historical summary of past testing, not a current reading. Mormon Trail Lake has a water quality grade of B (Good). Bacteria levels can spike quickly after heavy rain, so always check Iowa's current beach and health-department advisories before you swim.
What is the water temperature of Mormon Trail Lake?
- Mormon Trail Lake typically sits around 71°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 Mormon Trail Lake?
- No published bathymetric survey covers Mormon Trail Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 25 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 33 acres.
Explore Mormon Trail Lake across LakeQuality
More Iowa Lake Rankings
Other Grade B Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
63 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_WQX63 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)