Mormon Trail Lake
Adair County, Iowa33 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Mormon Trail Lake. Here is what has been measured.
- Eutrophic
- Impaired · Mercury
- 25 ft max depth
Mormon Trail Lake in Adair County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 6.2 ft visibility. Phosphorus: 25 µg/L. Chlorophyll-a (algae): 9.7 µg/L. Surface area: 33 acres.
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. 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. Methodology: how these readings are compared.
Mormon Trail Lake covers about 33 acres in Adair County. For a place on the water, look through cabin and lake-house rentals near Mormon Trail Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
Swimming conditions
Readings onlyRecreation use not supported
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.
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.
Whether Mormon Trail 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 Mormon Trail Lake
These are the measurements Iowa DNR publishes for Mormon Trail Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 6.2 ft. Phosphorus 25 µg/L. Chlorophyll-a 9.7 µg/L. TSI 51.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 6.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 25µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 9.7µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 51 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Mormon Trail Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (71°F) to its warmest (82°F).
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
Max depth
~25 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
Watershed (drainage) area
1 sq mi
HydroLAKES / HydroSHEDS
Shoreline
1 mi
HydroLAKES / HydroSHEDS
Elevation
1,220 ft
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.
Stays via Stay22
Stays 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.
Top-rated places to stay near Mormon Trail Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Iowa’s top lakes →
Follow Mormon Trail Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Mormon Trail Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2020–2024).
Water clarity
Improving5 years
Phosphorus
Worsening+37.2 µg/L/yr4 years
Chlorophyll-a
Improving-1.14 µg/L/yr5 years
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
Designated uses not supporting: Recreation.
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.
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. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Mormon Trail Lake?
- Mormon Trail Lake in Adair County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. 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 is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Mormon Trail Lake is safe to swim in today is a call for Iowa's water agency and the county health department; check their current beach 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 lakes in Iowa
Other 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)
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)
Lake size & watershed from HydroLAKES (HydroSHEDS)