Weallup Lake
Snohomish County, WashingtonView mapDirections
Nutrients and algae sit mid-range for this region.
- Eutrophic
- Impaired · Nuisance exotic species
- #1 of 1 in the county
- Limited data
Weallup Lake in Snohomish County, Washington has a water quality grade of C (Fair). Phosphorus: 40 µg/L.
- Type
- Eutrophic
- Phosphorus
- 40 µg/L
- Trend
- ↓ Declining
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Watch Weallup Lake’s letter
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Weallup Lake is a productive, nutrient-rich eutrophic lake in Snohomish County, Washington. Water quality is graded C based on 1 sampling years through 2019. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, WA Ecology, last sampled 2019-04-29. Grade methodology: LakeQuality methodology.
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 C is nutrients and algae, not a swimming clearance. Weallup Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for nuisance exotic species. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 40 µg/L. TSI 57. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 40 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 57 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Fishing Weallup Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +2.92 µg/L/yr | 2 |
EPA Impairment Status
Weallup Lake is officially listed as impaired under Clean Water Act §303(d) in the 2018 EPA reporting cycle (IR category 4C).
Causes of impairment
Source: EPA ATTAINS assessment unit WA17110019001059_001_001 · Official waterbody report · Matched by proximity (1.99 km)
County Ranking
Ranked #1 of 1 lakes in Snohomish County
Nearby Lakes in Snohomish County
Frequently asked questions about Weallup Lake
Where is Weallup Lake?
- Weallup Lake is a lake in Snohomish County, Washington. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Weallup Lake?
- Weallup Lake in Snohomish County, Washington has a water quality grade of C (Fair). Phosphorus: 40 µg/L.
Is Weallup Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Weallup Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for nuisance exotic species. Check local advisories before you swim.
Explore Weallup Lake across LakeQuality
Species activity outlook by water temperature and season
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Where this data comes from
22 measurements from 1 monitoring station, 2012–2019. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Tulalip Tribes (Tribal)
TRTUL_WQX22 samples · 2012–2019
Analytical methods
- Phosphorus, Total Ascorbic Acid Method
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