Newton Reservoir
Cache County, Utah297 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #1 of 9 in the county
Newton Reservoir in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 15.4 ft visibility. Phosphorus: 26 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Surface area: 297 acres.
- Clarity
- 15.4 ft
- Area
- 297 acres
- Type
- Oligotrophic
- Phosphorus
- 26 µg/L
- Chlorophyll-a
- 1.7 µg/L
- Trend
- ↓ Declining
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Watch Newton Reservoir’s letter
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Newton Reservoir is a 297-acre cold, clear oligotrophic lake in Cache County, Utah. Water quality is graded A based on 2 sampling years through 2021. Overall water quality is declining over recent sampling years. Compared to the 8 other monitored lakes in Cache County, Newton Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2021-10-06. Grade methodology: LakeQuality methodology.
What Newton Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water15.4 ft of visibility
Swimming Safety
Grade onlyLow algae
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 A is nutrients and algae, not a swimming clearance. Newton Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), temperature. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Crystal clear, you can see 15.4 ft down. Phosphorus 26 µg/L. Chlorophyll-a 1.7 µg/L. TSI 42. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15.4 ft | Not graded |
| Phosphorus | 26 µg/L | Good |
| Chlorophyll-a (Algae) | 1.7 µg/L | Good |
| Trophic State Index (TSI) | 42 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 297 acres |
No bathymetric survey has been published for Newton Reservoir, so its depth is not documented here.
Fishing Newton Reservoir
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.034 m/yr | 6 |
| Phosphorus | ↓ Declining | +3.5 µg/L/yr | 2 |
| Chlorophyll-a | ↓ Declining | +0.7 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Newton Reservoir is a man-made reservoir impounded by the Newton Dam (completed 1946), built primarily for irrigation on the Clarkston Creek; earth-type dam, 104 ft tall and 3,340 ft long.
- Surface area
- 297 ac
- Normal storage
- 5,594 ac-ft
- Max storage
- 5,594 ac-ft
- Drainage area
- 55.99 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID UT10129 · Operator website
EPA Impairment Status
Newton 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-16010202-013_00 · Official waterbody report
County Ranking
Ranked #1 of 9 lakes in Cache County
Nearby Lakes in Cache County
Frequently asked questions about Newton Reservoir
Where is Newton Reservoir?
- Newton Reservoir is a lake in Cache County, Utah. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Newton Reservoir?
- Newton Reservoir in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 15.4 ft visibility. Phosphorus: 26 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Surface area: 297 acres.
Is Newton Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Newton Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), temperature. Check local advisories before you swim.
Explore Newton Reservoir across LakeQuality
4 thermal springs within 15.2 mi, nearest Gancheff Spring
Species activity outlook by water temperature and season
Where to stay at Utah's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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Where this data comes from
127 measurements from 2 monitoring stations, 2014–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX127 samples · 2014–2021
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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