Lake Monroe
Union County, North Carolina118 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- #2 of 3 in the county
- 34 ft max depth
- Limited data
Lake Monroe in Union County, North Carolina has a water quality grade of F (Algae-prone). Phosphorus: 110 µg/L. Chlorophyll-a (algae): 62 µg/L. Surface area: 118 acres.
- Max depth
- ~34 ft est.
- Area
- 118 acres
- Type
- Hypereutrophic
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Stays near Lake Monroe
Compare lakeside cabins, hotels, and vacation rentals near Lake Monroe in Union County, North Carolina — 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Lake Monroe are listed below.
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Watch Lake Monroe’s letter
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Lake Monroe is a 118-acre highly nutrient-loaded hypereutrophic lake in Union County, North Carolina with an estimated average depth of about 34 feet. Water quality is graded F based on 2 sampling years through 2021. Compared to the 2 other monitored lakes in Union County, Lake Monroe ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, NCDEQ, last sampled 2021-09-29. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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 F is nutrients and algae, not a swimming clearance. Lake Monroe is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, pH / acidity, temperature. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
No clarity data. Phosphorus 110 µg/L. Chlorophyll-a 62 µg/L. TSI 72. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 110 µg/L | Poor |
| Chlorophyll-a (Algae) | 62 µg/L | Poor |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~34 ft est. |
| Average Depth | ~10 ft est. |
| Surface Area | 118 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. North Carolina has not published bathymetry for Lake Monroe.
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 Monroe
Reservoir Info (USACE NID)
Lake Monroe is a man-made reservoir impounded by the Lake Monroe Dam (completed 1955), built primarily for recreation on the Richardson Creek; earth-type dam, 46 ft tall and 770 ft long.
- Surface area
- 118 ac
- Normal storage
- 1,765 ac-ft
- Max storage
- 2,721 ac-ft
- Drainage area
- 9.58 sq mi
- Hazard class
- High
- Owner
- City of Monroe
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID NC00535 · Operator website
EPA Impairment Status
Lake Monroe is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NC13-17-36-4-(2) · Official waterbody report · Matched by proximity (0.41 km)
County Ranking
Ranked #2 of 3 lakes in Union County
Nearby Lakes in Union County
Frequently asked questions about Lake Monroe
Where is Lake Monroe?
- Lake Monroe is a lake in Union County, North Carolina. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Monroe?
- Lake Monroe in Union County, North Carolina has a water quality grade of F (Algae-prone). Phosphorus: 110 µg/L. Chlorophyll-a (algae): 62 µg/L. Surface area: 118 acres.
Is Lake Monroe safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Lake Monroe is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, pH / acidity, temperature. Check local advisories before you swim.
How deep is Lake Monroe?
- No published bathymetric survey covers Lake Monroe, 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 118 acres.
Explore Lake Monroe across LakeQuality
Species activity outlook by water temperature and season
Where to stay at North Carolina's top lakes, each with its grade
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Where this data comes from
27 measurements from 2 monitoring stations, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Carolina Dept of Environmental Quality NCDEQ-DWR WQX
21NC03WQ27 samples · 2021
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 2130 B ~ Nephelometric Method
Monitoring station identifiers (2)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)