Lake Mission Viejo
Lake Mission Viejo in Orange County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 9.5 ft visibility. Surface area: 150 acres.
- Clarity
- 9.5 ft
- Area
- 150 acres
Why Lake Mission Viejo has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Lake Mission Viejo, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by your state environmental agency and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Lake Mission Viejo is a 150-acre lake in Orange County, California.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-07-05. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Lake Mission Viejo
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Moderate clarity, visible to about 9.5 ft. Trophic State Index: 45.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Lake Mission Viejo
Compare lakeside cabins, hotels, and vacation rentals near Lake Mission Viejo in Orange County, California — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Lake Mission Viejo
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 150 acres |
No bathymetric survey has been published for Lake Mission Viejo, so its depth is not documented here.
Fishing Lake Mission Viejo
Reservoir Info (USACE NID)
Lake Mission Viejo is a man-made reservoir impounded by the Lake Mission Viejo (completed 1976), built primarily for water supply on the Oso Creek; earth-type dam, 123 ft tall and 1,750 ft long.
- Surface area
- 150 ac
- Max storage
- 4,300 ac-ft
- Drainage area
- 3.6 sq mi
- Hazard class
- High
- Owner
- Lake Mission Viejo Association, Inc.
All listed purposes: Water Supply;Recreation.
Source: USACE National Inventory of Dams, NID ID CA01122 · Operator website
Graded lakes near Lake Mission Viejo
Lake Mission Viejo has no grade, but these lakes within a short drive do.
Nearby Lakes in Orange County
Frequently asked questions about Lake Mission Viejo
Where is Lake Mission Viejo?
- Lake Mission Viejo is a lake in Orange County, California. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for Lake Mission Viejo?
- Lake Mission Viejo in Orange County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 9.5 ft visibility. Surface area: 150 acres.
Is Lake Mission Viejo safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Lake Mission Viejo is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Lake Mission Viejo across LakeGrade
More California Lake Rankings
Other Lakes in California
Mesotrophic Lakes in California
Where this data comes from
4 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- North American Lake Management Society
NALMS4 samples · 2020–2023
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.