Lake Marie
Mercer County, Missouri30 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Mesotrophic
- #1 of 1 in the county
- 34 ft max depth
Lake Marie in Mercer County, Missouri has a water quality grade of A (Excellent). Water clarity: 7.8 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 30 acres.
- Clarity
- 7.8 ft
- Typical in August
- 83°F
- Max depth
- ~34 ft est.
- Area
- 30 acres
- Type
- Mesotrophic
- Phosphorus
- 13 µg/L
- Chlorophyll-a
- 2.7 µg/L
- Trend
- ↑ Improving
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Watch Lake Marie’s letter
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Lake Marie is a 30-acre mesotrophic lake in Mercer County, Missouri with an estimated average depth of about 34 feet. Water quality is graded A based on 2 sampling years through 2023. Overall water quality is improving over recent sampling years.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2023-08-01. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLow algae
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.
The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 7.8 ft. Phosphorus 13 µg/L. Chlorophyll-a 2.7 µg/L. TSI 43. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.8 ft | Not graded |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | 2.7 µg/L | Good |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Water Temperature
Lake Marie typically sits around 83°F at the surface in August. Summer average is about 81°F. Usually warmest in Jul (about 83°F) and coldest in May (about 70°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 12 field readings (2021–2023) via the EPA Water Quality Portal. See the full Lake Marie water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~34 ft est. |
| Average Depth | ~12 ft est. |
| Surface Area | 30 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Missouri has not published bathymetry for Lake Marie.
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 Lake Marie
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.955 m/yr | 3 |
| Phosphorus | ↑ Improving | -2.05 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -1.1 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Lake Marie is a man-made reservoir impounded by the Lake Marie Dam (completed 1981), built primarily for recreation on the POPS BRANCH; earth-type dam, 50 ft tall and 1,100 ft long.
- Surface area
- 30 ac
- Normal storage
- 882 ac-ft
- Max storage
- 970 ac-ft
- Drainage area
- 0.53 sq mi
- Hazard class
- High
- Owner
- LAKE MARIE HOA
Source: USACE National Inventory of Dams, NID ID MO10154 · Operator website
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Lake Marie under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Twin Lakes WwtfMercer · 0.2 mi away · NPDES MO0129216Recent violation
- Mercer WwtfMercer · 2.2 mi away · NPDES MO0056057Recent 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 1 lakes in Mercer County
Nearby Lakes in Mercer County
Frequently asked questions about Lake Marie
Where is Lake Marie?
- Lake Marie is a lake in Mercer County, Missouri. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Marie?
- Lake Marie in Mercer County, Missouri has a water quality grade of A (Excellent). Water clarity: 7.8 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 30 acres.
Is Lake Marie safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Lake Marie?
- Lake Marie typically sits around 83°F at the surface in August, from 12 EPA Water Quality Portal field readings (2021–2023). That is a typical value for the month, not a live reading.
How deep is Lake Marie?
- No published bathymetric survey covers Lake Marie, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 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 30 acres.
Explore Lake Marie across LakeQuality
More Missouri Lake Rankings
Other Grade A Lakes in Missouri
Mesotrophic Lakes in Missouri
Where this data comes from
60 measurements from 1 monitoring station, 2021–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC60 samples · 2021–2023
Analytical methods
- Depth, Secchi disk in meters
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)