Lost Valley Lake
Gasconade County, Missouri39 acresView mapDirections
Nutrients and algae sit mid-range for this region.
- Mesotrophic
- #2 of 3 in the county
- 44 ft max depth
Lost Valley Lake in Gasconade County, Missouri has a water quality grade of C (Fair). Water clarity: 3.9 ft visibility. Phosphorus: 22.7 µg/L. Chlorophyll-a (algae): 6.6 µg/L. Surface area: 39 acres.
- Clarity
- 3.9 ft
- Typical in August
- 84°F
- Max depth
- ~44 ft est.
- Area
- 39 acres
- Type
- Mesotrophic
- Phosphorus
- 22.7 µg/L
- Chlorophyll-a
- 6.6 µg/L
- Trend
- ↑ Improving
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Watch Lost Valley Lake’s letter
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Lost Valley Lake is a 39-acre mesotrophic lake in Gasconade County, Missouri with an estimated average depth of about 44 feet. Water quality is graded C based on 2 sampling years through 2022. Overall water quality is improving over recent sampling years. Compared to the 2 other monitored lakes in Gasconade County, Lost Valley Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2022-09-22. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyModerate
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. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Murky, only visible to about 3.9 ft. Phosphorus 22.7 µg/L. Chlorophyll-a 6.6 µg/L. TSI 52. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.9 ft | Not graded |
| Phosphorus | 22.7 µg/L | Fair |
| Chlorophyll-a (Algae) | 6.6 µg/L | Fair |
| Trophic State Index (TSI) | 52 | Mesotrophic |
Moderate nutrients, good water quality
Water Temperature
Lost Valley Lake typically sits around 84°F at the surface in August. Summer average is about 84°F. Usually warmest in Jul (about 86°F) and coldest in May (about 75°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 16 field readings (2019–2022) via the EPA Water Quality Portal. See the full Lost Valley Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~44 ft est. |
| Average Depth | ~16 ft est. |
| Surface Area | 39 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 Lost Valley 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.
Fishing Lost Valley Lake
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.06 m/yr | 3 |
| Phosphorus | ↑ Improving | -1.55 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -1.8 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Lost Valley Lake is a man-made reservoir impounded by the Lost Valley Lake Dam (completed 1974), built primarily for recreation on the TR-BIG BRCH-BOEUF CREEK; earth-type dam, 30 ft tall.
- Surface area
- 39 ac
- Normal storage
- 455 ac-ft
- Max storage
- 626 ac-ft
- Drainage area
- 1,300 sq mi
- Hazard class
- High
- Owner
- RON DOLPH
Source: USACE National Inventory of Dams, NID ID MO30757 · Operator website
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Lost Valley Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Lost Valley Lake ResortOwensville · 0.2 mi away · NPDES MO0103161Recent violation
- Country Living Apartments WwtfOwensville · 2.1 mi away · NPDES MO0134376Recent 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 #2 of 3 lakes in Gasconade County
Nearby Lakes With Higher Grades
Lost Valley Lake holds Grade C. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Gasconade County
Frequently asked questions about Lost Valley Lake
Where is Lost Valley Lake?
- Lost Valley Lake is a lake in Gasconade County, Missouri. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lost Valley Lake?
- Lost Valley Lake in Gasconade County, Missouri has a water quality grade of C (Fair). Water clarity: 3.9 ft visibility. Phosphorus: 22.7 µg/L. Chlorophyll-a (algae): 6.6 µg/L. Surface area: 39 acres.
Is Lost Valley Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Lost Valley Lake?
- Lost Valley Lake typically sits around 84°F at the surface in August, from 16 EPA Water Quality Portal field readings (2019–2022). That is a typical value for the month, not a live reading.
How deep is Lost Valley Lake?
- No published bathymetric survey covers Lost Valley Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 44 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 39 acres.
Explore Lost Valley Lake across LakeQuality
More Missouri Lake Rankings
Other Grade C Lakes in Missouri
Mesotrophic Lakes in Missouri
Where this data comes from
59 measurements from 2 monitoring stations, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC58 samples · 2020–2022 - Missouri Dept. of Natural Resources
MDNR1 sample · 2021
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
- Nitrogen and Phosphorus, Total, Whole-water, Alkaline Persulfate Digest
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)