San Gregorio Deep Lake
Rio Arriba County, New Mexico33 acresView mapDirections
Not enough samples to grade — 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. No letter yet. Here is what we do have.
- Impaired · Nutrients (phosphorus, nitrogen)
- Limited data
San Gregorio Deep Lake in Rio Arriba County, New Mexico is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.3 ft visibility. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 33 acres.
- Clarity
- 4.3 ft
- Area
- 33 acres
- Chlorophyll-a
- 8.5 µg/L
- Trend
- ↓ Declining
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Watch San Gregorio Deep Lake’s letter
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Why San Gregorio Deep Lake has no grade
We grade a lake only when the monitoring record supports a letter: 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 San Gregorio Deep Lake, 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 and algae (chlorophyll-a), but not phosphorus.
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 NMED and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
San Gregorio Deep Lake is a 33-acre lake in Rio Arriba County, New Mexico. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, NMED, last sampled 2014-09-22. Grade methodology: LakeQuality methodology.
What San Gregorio Deep Lake is good for
From access and monitoring records, not editorial picks.
- Camping1 public campground nearby
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. San Gregorio Deep Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water quality measurements for San Gregorio Deep Lake
These readings exist but are not enough for an A–F grade — see why.
Murky, only visible to about 4.3 ft. Chlorophyll-a 8.5 µg/L. TSI 54.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.3 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 8.5 µg/L | Not graded |
| Trophic State Index (TSI) | 54 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 33 acres |
No bathymetric survey has been published for San Gregorio Deep Lake, so its depth is not documented here.
Recreation & Access
Public campgrounds near San Gregorio Deep Lake
- Clear Creek4.9 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Fishing San Gregorio Deep Lake
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.077 m/yr | 3 |
| Chlorophyll-a | ↓ Declining | +2.34 µg/L/yr | 3 |
Reservoir Info (USACE NID)
San Gregorio Deep Lake is a man-made reservoir impounded by the San Gregorio Dam (completed 1947), built primarily for irrigation on the Clear Creek; earth-type dam, 28 ft tall and 1,074 ft long.
- Surface area
- 33 ac
- Normal storage
- 254 ac-ft
- Max storage
- 500 ac-ft
- Drainage area
- 3.6 sq mi
- Hazard class
- High
- Owner
- NACIMIENTO COMMUNITY IRRIGATION COMPANY AND NMDGF
All listed purposes: Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID NM00185 · Operator website · Matched by proximity (0.24 km)
EPA Impairment Status
San Gregorio Deep Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit NM-2106.B_10 · Official waterbody report · Matched by proximity (0.11 km)
Graded lakes near San Gregorio Deep Lake
San Gregorio Deep Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Rio Arriba County
Frequently asked questions about San Gregorio Deep Lake
Where is San Gregorio Deep Lake?
- San Gregorio Deep Lake is a lake in Rio Arriba County, New Mexico. LakeQuality has not rated this lake (UNRATED) — 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.
What is the water quality grade for San Gregorio Deep Lake?
- San Gregorio Deep Lake in Rio Arriba County, New Mexico is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.3 ft visibility. Chlorophyll-a (algae): 8.5 µg/L. Surface area: 33 acres.
Is San Gregorio Deep Lake safe to swim in?
- The letter is not a swimming clearance. San Gregorio Deep Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Are there campgrounds on San Gregorio Deep Lake?
- San Gregorio Deep Lake has 1 public campground from USGS The National Map within 5 km, including Clear Creek. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore San Gregorio Deep Lake across LakeQuality
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Where this data comes from
9 measurements from 1 monitoring station, 2013–2014. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- NM Environmental Dept./SWQB
21NMEX_WQX9 samples · 2013–2014
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
Impairment status from EPA ATTAINS 303(d) database
Public campgrounds from USGS The National Map Structures, within about 3 miles