Banks Lake
Grant County, Washington27,000 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- #3 of 4 in the county
- 124 ft max depth
- Public access
Banks Lake in Grant County, Washington has a water quality grade of A (Excellent). Water clarity: 19.4 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 27000 acres.
- Clarity
- 19.4 ft
- Max depth
- ~124 ft est.
- Area
- 27,000 acres
- Type
- Oligotrophic
- Phosphorus
- 13 µg/L
- Chlorophyll-a
- 1.3 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Watch Banks Lake’s letter
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Banks Lake is a 27,000-acre cold, clear oligotrophic lake in Grant County, Washington with an estimated average depth of about 124 feet. Water quality is graded A based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 4 public boat landings. Compared to the 3 other monitored lakes in Grant County, Banks Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, WA Ecology, last sampled 2024-08-07. Grade methodology: LakeQuality methodology.
What Banks Lake is good for
From access and monitoring records, not editorial picks.
- Clear water19.4 ft of visibility
- Boat launch4 documented ramps
- Big water27,000 acres
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. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Crystal clear, you can see 19.4 ft down. Phosphorus 13 µg/L. Chlorophyll-a 1.3 µg/L. TSI 36. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 19.4 ft | Not graded |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | 1.3 µg/L | Good |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~124 ft est. |
| Average Depth | ~27 ft est. |
| Surface Area | 27,000 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Washington has not published bathymetry for Banks 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
- Steamboat Rock State ParkPublic
- Barker CanyonPublic
- Coulee Playland ResortSemi-private
- Sunbanks ResortSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Banks Lake
Water Quality Trend: ↓ Declining
Based on 12 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.029 m/yr | 11 |
| Phosphorus | ↓ Declining | +5.96 µg/L/yr | 8 |
| Chlorophyll-a | ↓ Declining | +0.04 µg/L/yr | 12 |
Reservoir Info (USACE NID)
Banks Lake is a man-made reservoir impounded by the North Dam (completed 1951), built primarily for flood risk reduction on the Upper Grand Coulee River; earth-type dam, 145 ft tall and 1,450 ft long.
- Surface area
- 27,000 ac
- Normal storage
- 1,275,000 ac-ft
- Max storage
- 1,275,000 ac-ft
- Drainage area
- 263 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Flood Risk Reduction;Irrigation;Navigation;Hydroelectric.
Source: USACE National Inventory of Dams, NID ID WA00266 · Operator website
County Ranking
Ranked #3 of 4 lakes in Grant County
Nearby Lakes in Grant County
Frequently asked questions about Banks Lake
Where is Banks Lake?
- Banks Lake is a lake in Grant County, Washington. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Banks Lake?
- Banks Lake in Grant County, Washington has a water quality grade of A (Excellent). Water clarity: 19.4 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 1.3 µg/L. Surface area: 27000 acres.
Is Banks Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
How deep is Banks Lake?
- No published bathymetric survey covers Banks Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 124 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 27000 acres.
Are there boat ramps on Banks Lake?
- Banks Lake has 4 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Steamboat Rock State Park, Barker Canyon, Coulee Playland Resort, Sunbanks Resort. Public access is listed as yes.
Explore Banks Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Washington's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
Washington's cleanest and most-polluted lakes, ranked
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Other Grade A Lakes in Washington
Oligotrophic Lakes in Washington
Where this data comes from
88 measurements from 2 monitoring stations, 2012–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX88 samples · 2012–2024
Analytical methods
- Depth, Secchi disk depth
- Zebra/Quagga Mussel APHA 10200G Modified
- Phosphorus by Single Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory