Porcupine Reservoir
Cache County, UtahView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from B at the last regrade
- Mesotrophic
- #6 of 9 in the county
Porcupine Reservoir in Cache County, Utah has a water quality grade of C (Fair). Water clarity: 8.5 ft visibility. Phosphorus: 13.3 µg/L. Chlorophyll-a (algae): 3.8 µg/L.
- Clarity
- 8.5 ft
- Type
- Mesotrophic
- Phosphorus
- 13.3 µg/L
- Chlorophyll-a
- 3.8 µg/L
- Trend
- ↑ Improving
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Watch Porcupine Reservoir’s letter
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Porcupine Reservoir is a mesotrophic lake in Cache County, Utah. Water quality is graded C based on 2 sampling years through 2021. Overall water quality is improving over recent sampling years. Compared to the 8 other monitored lakes in Cache County, Porcupine Reservoir ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2021-09-13. 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)
Moderate clarity, visible to about 8.5 ft. Phosphorus 13.3 µg/L. Chlorophyll-a 3.8 µg/L. TSI 44. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.5 ft | Not graded |
| Phosphorus | 13.3 µg/L | Good |
| Chlorophyll-a (Algae) | 3.8 µg/L | Fair |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Fishing Porcupine Reservoir
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.198 m/yr | 4 |
| Phosphorus | ↑ Improving | -4.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -1.35 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Porcupine Reservoir is a man-made reservoir impounded by the Porcupine (completed 1962), built primarily for irrigation on the East Fk Little Bear River; earth-type dam, 181 ft tall and 665 ft long.
- Normal storage
- 13,000 ac-ft
- Max storage
- 15,000 ac-ft
- Drainage area
- 72 sq mi
- Hazard class
- High
- Owner
- PORCUPINE RESERVOIR COMPANY
Source: USACE National Inventory of Dams, NID ID UT00251 · Operator website
County Ranking
Ranked #6 of 9 lakes in Cache County
Nearby Lakes With Higher Grades
Porcupine Reservoir holds Grade C. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Cache County
Frequently asked questions about Porcupine Reservoir
Where is Porcupine Reservoir?
- Porcupine Reservoir is a lake in Cache County, Utah. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Porcupine Reservoir?
- Porcupine Reservoir in Cache County, Utah has a water quality grade of C (Fair). Water clarity: 8.5 ft visibility. Phosphorus: 13.3 µg/L. Chlorophyll-a (algae): 3.8 µg/L.
Is Porcupine Reservoir safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Porcupine Reservoir across LakeQuality
More Utah Lake Rankings
Other Grade C Lakes in Utah
Mesotrophic Lakes in Utah
Where this data comes from
142 measurements from 1 monitoring station, 2015–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX142 samples · 2015–2021
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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.