Lost Valley Lake is a 39-acre productive, nutrient-rich eutrophic lake in Gasconade County, Missouri. Water quality is graded C based on 3 sampling years through 2022. Overall water quality is improving over recent sampling years. Compared to the 3 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: LakeGrade methodology.
Watch Lost Valley Lake water quality
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 3.9 ft. Phosphorus level: 22.7 µg/L. Chlorophyll-a: 7.2 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.9 ft | D |
| Phosphorus | 22.7 µg/L | B |
| Chlorophyll-a (Algae) | 7.2 µg/L | B |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 39 acres |
Where to stay near Lost Valley Lake
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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 | -0.9 µg/L/yr | 3 |
Water Temperature
Lost Valley Lake averages about 84°F at the surface in summer, 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 →
Location
County Ranking
Ranked #2 of 4 lakes in Gasconade County
Cleaner Lakes Within 30 Miles
Lost Valley Lake holds Grade C. 2 nearby lakes hold higher grades.
- AAlpine LakeWarren County · 25.3 mi · Two grade letters higher (C → A)
- BSeetal LakeGasconade County · 14.8 mi · Higher grade (C → B)
Nearby Lakes in Gasconade County
Explore Lost Valley Lake across LakeGrade
More Missouri Lake Rankings
Other Grade C Lakes in Missouri
Eutrophic Lakes in Missouri
More records, surveys & data sources
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
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-09-22
Monitoring stations: 2