Fourmile Lake
Klamath County, Oregon962 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- #6 of 17 in the county
- 47 ft max depth
- Public access
- Limited data
Fourmile Lake in Klamath County, Oregon has a water quality grade of A (Excellent). Chlorophyll-a (algae): 0.5 µg/L. Surface area: 962 acres.
- Max depth
- ~47 ft est.
- Area
- 962 acres
- Type
- Oligotrophic
- Chlorophyll-a
- 0.5 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Watch Fourmile Lake’s letter
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Fourmile Lake is a 962-acre cold, clear oligotrophic lake in Klamath County, Oregon with an estimated average depth of about 47 feet. Water quality is graded A based on 1 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 16 other monitored lakes in Klamath County, Fourmile Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Oregon DEQ, last sampled 2025-10-01. Grade methodology: LakeQuality methodology.
What Fourmile Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Camping1 public campground 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)
No clarity data. Chlorophyll-a 0.5 µg/L. TSI 23. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 0.5 µg/L | Good |
| Trophic State Index (TSI) | 23 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~47 ft est. |
| Surface Area | 962 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Oregon has not published bathymetry for Fourmile Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Fourmile Lake CampgroundPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Public campgrounds near Fourmile Lake
- Fourmile Lake Campground0.3 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 Fourmile Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Chlorophyll-a | ↓ Declining | +0.1 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Fourmile Lake is a man-made reservoir impounded by the Fourmile Lake Dam (completed 1922), built primarily for flood risk reduction on the Fourmile Creek; rockfill-type dam, 25 ft tall and 660 ft long.
- Surface area
- 962 ac
- Normal storage
- 15,600 ac-ft
- Max storage
- 15,600 ac-ft
- Drainage area
- 10.41 sq mi
- Hazard class
- Low
- Owner
- MEDFORD IRRIGATION DISTRICT
All listed purposes: Flood Risk Reduction;Irrigation.
Source: USACE National Inventory of Dams, NID ID OR00022 · Operator website
County Ranking
Ranked #6 of 17 lakes in Klamath County
Nearby Lakes in Klamath County
Frequently asked questions about Fourmile Lake
Where is Fourmile Lake?
- Fourmile Lake is a lake in Klamath County, Oregon. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Fourmile Lake?
- Fourmile Lake in Klamath County, Oregon has a water quality grade of A (Excellent). Chlorophyll-a (algae): 0.5 µg/L. Surface area: 962 acres.
Is Fourmile Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
How deep is Fourmile Lake?
- No published bathymetric survey covers Fourmile Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 47 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 962 acres.
Are there boat ramps on Fourmile Lake?
- Fourmile Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Fourmile Lake Campground. Public access is listed as yes.
Are there campgrounds on Fourmile Lake?
- Fourmile Lake has 1 public campground from USGS The National Map within 5 km, including Fourmile Lake Campground. 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 Fourmile Lake across LakeQuality
23.4 mi away · 173 ft
Species activity outlook by water temperature and season
Where to stay at Oregon's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
Oregon's cleanest and most-polluted lakes, ranked
Planning a trip around Crater Lake?
Fourmile Lake is about 34 miles from Crater Lake National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Crater Lake →More Oregon Lake Rankings
Other Grade A Lakes in Oregon
Oligotrophic Lakes in Oregon
Where this data comes from
8 measurements from 1 monitoring station, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Department of Environmental Quality - State of Oregon
OREGONDEQ8 samples · 2024–2025
Analytical methods
- 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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles