Lake Nehai Tonkayea
Chariton County, Missouri250 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Oligotrophic
- a waterflea
- #1 of 3 in the county
- 45 ft max depth
Lake Nehai Tonkayea in Chariton County, Missouri has a water quality grade of A (Excellent). Water clarity: 8 ft visibility. Phosphorus: 10 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 250 acres.
- Clarity
- 8 ft
- Typical in August
- 83°F
- Max depth
- ~45 ft est.
- Area
- 250 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
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Watch Lake Nehai Tonkayea’s letter
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Lake Nehai Tonkayea is a 250-acre cold, clear oligotrophic lake in Chariton County, Missouri with an estimated average depth of about 45 feet. Water quality is graded A based on 2 sampling years through 2023. Overall water quality is improving over recent sampling years. Compared to the 2 other monitored lakes in Chariton County, Lake Nehai Tonkayea ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2023-08-10. 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 8 ft. Phosphorus 10 µg/L. Chlorophyll-a 1.3 µg/L. TSI 39. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8 ft | Not graded |
| Phosphorus | 10 µg/L | Good |
| Chlorophyll-a (Algae) | 1.3 µg/L | Good |
| Trophic State Index (TSI) | 39 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Water Temperature
Lake Nehai Tonkayea typically sits around 83°F at the surface in August. Summer average is about 82°F. Usually warmest in Jul (about 83°F) and coldest in May (about 69°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 19 field readings (2015–2023) via the EPA Water Quality Portal. See the full Lake Nehai Tonkayea water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~45 ft est. |
| Average Depth | ~15 ft est. |
| Surface Area | 250 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 Nehai Tonkayea.
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 Nehai Tonkayea
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.115 m/yr | 3 |
| Phosphorus | ↑ Improving | -0.35 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -0.4 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Lake Nehai Tonkayea is a man-made reservoir impounded by the Nehai Tonkayea Lake Dam (completed 1970), built primarily for recreation on the TR-MUSSEL FORK; earth-type dam, 65 ft tall and 1,700 ft long.
- Surface area
- 250 ac
- Normal storage
- 5,417 ac-ft
- Max storage
- 9,100 ac-ft
- Drainage area
- 1.48 sq mi
- Hazard class
- Low
- Owner
- NEHAI TONKAYEA POA
Source: USACE National Inventory of Dams, NID ID MO10627 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Lake Nehai Tonkayea under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Lake Nehai Tonkayea WwtpKeytesville · 0.2 mi away · NPDES MO0088510Recent 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 3 lakes in Chariton County
Nearby Lakes in Chariton County
Frequently asked questions about Lake Nehai Tonkayea
Where is Lake Nehai Tonkayea?
- Lake Nehai Tonkayea is a lake in Chariton 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 Nehai Tonkayea?
- Lake Nehai Tonkayea in Chariton County, Missouri has a water quality grade of A (Excellent). Water clarity: 8 ft visibility. Phosphorus: 10 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 250 acres.
Is Lake Nehai Tonkayea 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 Nehai Tonkayea?
- Lake Nehai Tonkayea typically sits around 83°F at the surface in August, from 19 EPA Water Quality Portal field readings (2015–2023). That is a typical value for the month, not a live reading.
How deep is Lake Nehai Tonkayea?
- No published bathymetric survey covers Lake Nehai Tonkayea, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 45 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 250 acres.
Explore Lake Nehai Tonkayea across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Missouri's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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Other Grade A Lakes in Missouri
Oligotrophic Lakes in Missouri
Where this data comes from
55 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
UMC55 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)