Oasis Ranch Upper Lake is a cold, clear oligotrophic lake in Audrain County, Missouri. Water quality is graded A based on 3 sampling years through 2024. Compared to the 3 other monitored lakes in Audrain County, Oasis Ranch Upper Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Good clarity, visible to about 14.4 ft. Phosphorus level: 12 µg/L. Chlorophyll-a: 1.8 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.4 ft | B |
| Phosphorus | 12 µg/L | A |
| Chlorophyll-a (Algae) | 1.8 µg/L | A |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Oasis Ranch Upper Lake
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Fishing Oasis Ranch Upper Lake
Location
County Ranking
Ranked #1 of 4 lakes in Audrain County
Nearby Lakes in Audrain County
Explore Oasis Ranch Upper Lake across LakeGrade
Species activity outlook by water temperature and season
Where to stay at Missouri's top lakes, each with its grade
Low nutrients, clear water, excellent for swimming
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More Missouri Lake Rankings
Other Grade A Lakes in Missouri
Warren County · Clarity: 12.6 ft
Jefferson County · Clarity: 12.9 ft
Iron County · Clarity: 13.1 ft
Washington County · Clarity: 11.1 ft
St. Francois County · Clarity: 14.3 ft
St. Francois County · Clarity: 16.3 ft
Oligotrophic Lakes in Missouri
More records, surveys & data sources
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Oasis Ranch Upper Lake under Clean Water Act (NPDES) discharge permits.
- Monroe County Pwsd 2 - Rush Hill WwtfRush Hill · 2.9 mi away · NPDES MO0126888
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)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-18
Monitoring stations: 1