Newcastle Reservoir
Iron County, UtahView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from D at the last regrade
- Eutrophic
- Impaired · Mercury
- #1 of 2 in the county
- Limited data
Newcastle Reservoir in Iron County, Utah has a water quality grade of C (Fair). Water clarity: 9.5 ft visibility. Phosphorus: 52 µg/L. Chlorophyll-a (algae): 89 µg/L.
- Clarity
- 9.5 ft
- Type
- Eutrophic
- Phosphorus
- 52 µg/L
- Chlorophyll-a
- 89 µg/L
- Trend
- ↓ Declining
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Watch Newcastle Reservoir’s letter
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Newcastle Reservoir is a productive, nutrient-rich eutrophic lake in Iron County, Utah. Water quality is graded C based on 1 sampling years through 2020. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Iron County, Newcastle Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2020-07-28. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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. Newcastle Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Moderate clarity, visible to about 9.5 ft. Phosphorus 52 µg/L. Chlorophyll-a 89 µg/L. TSI 60. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.5 ft | Not graded |
| Phosphorus | 52 µg/L | Fair |
| Chlorophyll-a (Algae) | 89 µg/L | Not graded |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Fishing Newcastle Reservoir
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.171 m/yr | 5 |
| Phosphorus | ↑ Improving | -1.81 µg/L/yr | 2 |
| Chlorophyll-a | ↓ Declining | +7.95 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Newcastle Reservoir is a man-made reservoir impounded by the Newcastle (completed 1956), built primarily for irrigation on the Pinto Creek; earth-type dam, 83 ft tall and 805 ft long.
- Normal storage
- 5,200 ac-ft
- Max storage
- 7,900 ac-ft
- Drainage area
- 134 sq mi
- Hazard class
- High
- Owner
- NEWCASTLE RESERVOIR COMPANY
Source: USACE National Inventory of Dams, NID ID UT00227 · Operator website
EPA Impairment Status
Newcastle Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-16030006-008_00 · Official waterbody report
County Ranking
Ranked #1 of 2 lakes in Iron County
Nearby Lakes in Iron County
Frequently asked questions about Newcastle Reservoir
Where is Newcastle Reservoir?
- Newcastle Reservoir is a lake in Iron County, Utah. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Newcastle Reservoir?
- Newcastle Reservoir in Iron County, Utah has a water quality grade of C (Fair). Water clarity: 9.5 ft visibility. Phosphorus: 52 µg/L. Chlorophyll-a (algae): 89 µg/L.
Is Newcastle Reservoir safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Newcastle Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
Explore Newcastle Reservoir across LakeQuality
More Utah Lake Rankings
Other Grade C Lakes in Utah
Eutrophic Lakes in Utah
Where this data comes from
97 measurements from 1 monitoring station, 2013–2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX97 samples · 2013–2020
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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database