Moses Lake
Grant County, WashingtonView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
- Mesotrophic
- Impaired · Temperature
- #4 of 4 in the county
- Public access
Moses Lake in Grant County, Washington has a water quality grade of B (Good). Phosphorus: 20 µg/L.
- Type
- Mesotrophic
- Phosphorus
- 20 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Watch Moses Lake’s letter
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Moses Lake is a mesotrophic lake in Grant County, Washington. Water quality is graded B based on 1 sampling years through 2022. 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 3 other monitored lakes in Grant County, Moses Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, WA Ecology, last sampled 2022-10-17. Grade methodology: LakeQuality methodology.
What Moses Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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 B is nutrients and algae, not a swimming clearance. Moses Lake is listed impaired under Clean Water Act §303(d) (IR 5) for temperature. Check local advisories before you swim.
Water Quality Grade: B (Good)
No clarity data. Phosphorus 20 µg/L. TSI 47. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 47 | Mesotrophic |
Moderate nutrients, good water quality
Recreation & Access
- Crab CreekPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Moses Lake
Water Quality Trend: ↓ Declining
Based on 10 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +3.2 µg/L/yr | 10 |
Reservoir Info (USACE NID)
Moses Lake is a man-made reservoir impounded by the Moses Lake South Dam (completed 1961), built primarily for irrigation on the Crab Creek; earth-type dam, 20 ft tall and 350 ft long.
- Normal storage
- 50,000 ac-ft
- Max storage
- 50,000 ac-ft
- Drainage area
- 2,689.36 sq mi
- Hazard class
- Low
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID WA00128 · Operator website
EPA Impairment Status
Moses Lake is officially listed as impaired under Clean Water Act §303(d) in the 2018 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WA47119A3I3_02_02 · Official waterbody report
County Ranking
Ranked #4 of 4 lakes in Grant County
Nearby Lakes in Grant County
Frequently asked questions about Moses Lake
Where is Moses Lake?
- Moses Lake is a lake in Grant County, Washington. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Moses Lake?
- Moses Lake in Grant County, Washington has a water quality grade of B (Good). Phosphorus: 20 µg/L.
Is Moses Lake safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Moses Lake is listed impaired under Clean Water Act §303(d) (IR 5) for temperature. Check local advisories before you swim.
Are there boat ramps on Moses Lake?
- Moses Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Crab Creek. Public access is listed as yes.
Explore Moses 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
Moderate nutrients, good water quality
Washington's cleanest and most-polluted lakes, ranked
More Washington Lake Rankings
Other Grade B Lakes in Washington
Mesotrophic Lakes in Washington
Where this data comes from
65 measurements from 1 monitoring station, 2012–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX65 samples · 2012–2022
Analytical methods
- Phosphorus by Single Reagent Colorimetry
- Turbidity by Nephelometry
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
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory