Mountain Island Lake
Gaston County, North Carolina3,235 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from B at the last regrade
- Mesotrophic
- #1 of 5 in the county
- 41 ft max depth
- Public access
- Limited data
Mountain Island Lake in Gaston County, North Carolina has a water quality grade of C (Fair). Phosphorus: 20 µg/L. Chlorophyll-a (algae): 6.5 µg/L. Surface area: 3235 acres.
- Max depth
- ~41 ft est.
- Area
- 3,235 acres
- Type
- Mesotrophic
- Public access
- Yes
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Watch Mountain Island Lake’s letter
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Mountain Island Lake is a 3,235-acre mesotrophic lake in Gaston County, North Carolina with an estimated average depth of about 41 feet. Water quality is graded C based on 1 sampling years through 2022. Limited fish-species data available. Public access is available with 4 public boat landings. Compared to the 4 other monitored lakes in Gaston County, Mountain Island Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, NCDEQ, last sampled 2022-09-13. Grade methodology: LakeQuality methodology.
What Mountain Island Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch4 documented ramps
- Big water3,235 acres
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 C is nutrients and algae, not a swimming clearance. Mountain Island Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pCBs. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 20 µg/L. Chlorophyll-a 6.5 µg/L. TSI 48. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 20 µg/L | Not graded |
| Chlorophyll-a (Algae) | 6.5 µg/L | Fair |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~41 ft est. |
| Average Depth | ~26 ft est. |
| Surface Area | 3,235 acres |
| Public Access | Yes |
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 Mountain Island 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.
Recreation & Access
- RiverbendPublic
- LuciaPublic
- Highwy 73Public
- Mt. Isle Harbor DrivePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Mountain Island Lake
Reservoir Info (USACE NID)
Mountain Island Lake is a man-made reservoir impounded by the Mountain Island (completed 1923), built primarily for hydroelectric on the Catawba River; gravity-type dam, 140 ft tall and 2,375 ft long.
- Surface area
- 3,235 ac
- Normal storage
- 45,970 ac-ft
- Max storage
- 45,970 ac-ft
- Drainage area
- 1,860 sq mi
- Hazard class
- High
- Owner
- Duke Energy
All listed purposes: Hydroelectric;Water Supply.
Source: USACE National Inventory of Dams, NID ID NC00787 · Operator website
EPA Impairment Status
Mountain Island Lake 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 NC11-(114) · Official waterbody report · Matched by proximity (0.14 km)
County Ranking
Ranked #1 of 5 lakes in Gaston County
Nearby Lakes in Gaston County
Frequently asked questions about Mountain Island Lake
Where is Mountain Island Lake?
- Mountain Island Lake is a lake in Gaston County, North Carolina. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mountain Island Lake?
- Mountain Island Lake in Gaston County, North Carolina has a water quality grade of C (Fair). Phosphorus: 20 µg/L. Chlorophyll-a (algae): 6.5 µg/L. Surface area: 3235 acres.
Is Mountain Island Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Mountain Island Lake is listed impaired under Clean Water Act §303(d) (IR 5) for pCBs. Check local advisories before you swim.
How deep is Mountain Island Lake?
- No published bathymetric survey covers Mountain Island Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 41 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 3235 acres.
Are there boat ramps on Mountain Island Lake?
- Mountain Island Lake has 4 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Riverbend, Lucia, Highwy 73, Mt. Isle Harbor Drive. Public access is listed as yes.
Explore Mountain Island Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at North Carolina's top lakes, each with its grade
Moderate nutrients, good water quality
North Carolina's cleanest and most-polluted lakes, ranked
More North Carolina Lake Rankings
Ranked by overall water quality grade
Top 25 by Secchi water clarity
Grade A/B + low algae filter
Panfish-rich, public access
Full state directory
Other Grade C Lakes in North Carolina
Mesotrophic Lakes in North Carolina
Where this data comes from
66 measurements from 6 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Carolina Dept of Environmental Quality NCDEQ-DWR WQX
21NC03WQ66 samples · 2022
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 2130 B ~ Nephelometric Method
Monitoring station identifiers (6)
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)
Named boat-access points from the USGS National Boat Ramps inventory