Lake Koocanusa
Lincoln County, Montana46,500 acresView mapDirections
Not Rated: one monitoring station are on record, but they measured water clarity only. LakeQuality’s A–F method grades total phosphorus, total nitrogen, chlorophyll-a, and turbidity; clarity is shown, not scored.
- Public access
- Limited data
Lake Koocanusa in Lincoln County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.8 ft visibility. Surface area: 46500 acres.
- Clarity
- 14.8 ft
- Area
- 46,500 acres
- Trend
- ↑ Improving
- Public access
- Yes
Stays via Stay22
Stays near Lake Koocanusa
Compare lakeside cabins, hotels, and vacation rentals near Lake Koocanusa in Lincoln County, Montana — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Lake Koocanusa
Prices for Sep 11–13, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Lake Koocanusa → · more Montana lake trips
Watch Lake Koocanusa’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
Why Lake Koocanusa has no grade
Lake Koocanusa has monitoring on record from one station, but only water clarity was measured. LakeQuality’s A–F letter uses total phosphorus, total nitrogen, chlorophyll-a, and turbidity against EPA National Lakes Assessment condition classes. With none of those grading measurements on record, Lake Koocanusa is Not Rated — not an F. Its 14.8-foot median from 33 readings collected 2013–2018 is still shown as clarity, but clarity alone cannot earn a letter.
Not Rated is EPA Integrated Reporting Category 3 — insufficient information. Everything below that has been measured is still reported on this page.
Sampling is run by Montana DEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Lake Koocanusa is a 46,500-acre lake in Lincoln County, Montana. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 3 public boat landings.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2018-10-23. Grade methodology: LakeQuality methodology.
What Lake Koocanusa is good for
From access and monitoring records, not editorial picks.
- Clear water14.8 ft of visibility
- Boat launch3 documented ramps
- Big water46,500 acres
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Lake Koocanusa
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 14.8 ft. TSI 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.8 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 46,500 acres |
| Public Access | Yes |
No bathymetric survey has been published for Lake Koocanusa, so its depth is not documented here.
Recreation & Access
- Souse Gulch Recreation AreaPublic
- Dunn CreekPublic
- RipleyPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake Koocanusa
Water Quality Trend: ↑ Improving
Based on 9 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.27 m/yr | 5 |
| Phosphorus | ↑ Improving | -0.3 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -0.23 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Lake Koocanusa is a man-made reservoir impounded by the Libby Dam (completed 1973), built primarily for hydroelectric on the Kootenai River; gravity-type dam, 422 ft tall and 2,890 ft long.
- Surface area
- 46,500 ac
- Normal storage
- 5,809,000 ac-ft
- Max storage
- 6,027,000 ac-ft
- Drainage area
- 8,985 sq mi
- Hazard class
- High
- Owner
- USACE - Seattle District
All listed purposes: Hydroelectric;Recreation;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID MT00652 · Operator website
Graded lakes near Lake Koocanusa
Lake Koocanusa has no grade, but these lakes within a short drive do.
Nearby Lakes in Lincoln County
Frequently asked questions about Lake Koocanusa
Where is Lake Koocanusa?
- Lake Koocanusa is a lake in Lincoln County, Montana. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Lake Koocanusa?
- Lake Koocanusa in Lincoln County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.8 ft visibility. Surface area: 46500 acres.
Is Lake Koocanusa safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
Are there boat ramps on Lake Koocanusa?
- Lake Koocanusa has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Souse Gulch Recreation Area, Dunn Creek, Ripley. Public access is listed as yes.
Explore Lake Koocanusa across LakeQuality
More Montana Lake Rankings
Other Lakes in Montana
Oligotrophic Lakes in Montana
Where this data comes from
33 measurements from 1 monitoring station, 2013–2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana DEQ WQPB
MDEQ_WQ_WQX33 samples · 2013–2018
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
Named boat-access points from the USGS National Boat Ramps inventory