Third Dam Lake
Cache County, Utah14 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Oligotrophic
- #5 of 9 in the county
- Limited data
Third Dam Lake in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 4.3 ft visibility. Phosphorus: 10.4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 14 acres.
- Clarity
- 4.3 ft
- Area
- 14 acres
- Type
- Oligotrophic
- Phosphorus
- 10.4 µg/L
- Chlorophyll-a
- 1.1 µg/L
- Trend
- → Stable
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Watch Third Dam Lake’s letter
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Third Dam Lake is a 14-acre cold, clear oligotrophic lake in Cache County, Utah. Water quality is graded A based on 1 sampling years through 2020. Water clarity is declining over recent sampling years. Compared to the 8 other monitored lakes in Cache County, Third Dam Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2020-09-22. Grade methodology: LakeQuality methodology.
What Third Dam Lake is good for
From access and monitoring records, not editorial picks.
- Camping4 public campgrounds nearby
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 A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Murky, only visible to about 4.3 ft. Phosphorus 10.4 µg/L. Chlorophyll-a 1.1 µg/L. TSI 42. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.3 ft | Not graded |
| Phosphorus | 10.4 µg/L | Not graded |
| Chlorophyll-a (Algae) | 1.1 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 | 14 acres |
No bathymetric survey has been published for Third Dam Lake, so its depth is not documented here.
Recreation & Access
Public campgrounds near Third Dam Lake
- Spring Hollow Campground0.5 km
- Bridger Campground1.0 km
- Guinavah-Malibu Campground2.0 km
- Green Canyon3.9 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 Third Dam Lake
Water Quality Trend: → Stable
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.2 m/yr | 2 |
| Chlorophyll-a | ↑ Improving | -3.4 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Third Dam Lake is a man-made reservoir impounded by the Logan No. 3 (completed 1924), built primarily for hydroelectric on the Logan River; concrete-type dam, 32 ft tall and 108 ft long.
- Surface area
- 14 ac
- Normal storage
- 40 ac-ft
- Hazard class
- Low
- Owner
- Logan, City of
All listed purposes: Hydroelectric;Irrigation;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID UT00310 · Operator website · Matched by proximity (0.03 km)
County Ranking
Ranked #5 of 9 lakes in Cache County
Nearby Lakes in Cache County
Frequently asked questions about Third Dam Lake
Where is Third Dam Lake?
- Third Dam Lake 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 Third Dam Lake?
- Third Dam Lake in Cache County, Utah has a water quality grade of A (Excellent). Water clarity: 4.3 ft visibility. Phosphorus: 10.4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 14 acres.
Is Third Dam Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Are there campgrounds on Third Dam Lake?
- Third Dam Lake has 4 public campgrounds from USGS The National Map within 5 km, including Spring Hollow Campground, Bridger Campground, Guinavah-Malibu Campground, Green Canyon. 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 Third Dam Lake across LakeQuality
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
9 measurements from 1 monitoring station, 2019–2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX9 samples · 2019–2020
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
Public campgrounds from USGS The National Map Structures, within about 3 miles