Derwentwater
Derwentwater in Cumbria and Lancashire, England has official water-quality measurements, not a LakeQuality A–F grade. Phosphorus: 7.9 µg/L. Chlorophyll-a (algae): 3.5 µg/L.
Why Derwentwater has no A–F grade
Derwentwater in England is published with the authority's own measurements, not a LakeQuality letter. official authority class; not a LakeQuality A–F letter Sampling here has recorded phosphorus and algae (chlorophyll-a), but not water clarity.
A letter on the LakeQuality scale would be an invention, not an official class. Everything below that has been measured is still reported on this page.
Monitoring: the Environment Agency (England).
Derwentwater is a lake in Cumbria and Lancashire County, England.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2026-05-14. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Derwentwater
These readings exist but do not meet the evidence bar for an A–F grade — see why.
No clarity data. Phosphorus level: 7.9 µg/L. Chlorophyll-a: 3.5 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 7.9 µg/L | Not graded |
| Chlorophyll-a (Algae) | 3.5 µg/L | Not graded |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Derwentwater
Compare lakeside cabins, hotels, and vacation rentals near Derwentwater in Cumbria and Lancashire, England — 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 Derwentwater
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Fishing Derwentwater
Frequently asked questions about Derwentwater
What is the water quality of Derwentwater?
- Derwentwater in Cumbria and Lancashire, England has official water-quality measurements, not a LakeQuality A–F grade. Phosphorus: 7.9 µg/L. Chlorophyll-a (algae): 3.5 µg/L.
Is Derwentwater safe to swim in?
- Derwentwater has official nutrient and clarity measurements, not a bacteria swim class and not a safety clearance. Algal blooms, currents, and depth are not covered. Always check local notices before swimming.
Explore Derwentwater across LakeGrade
More lakes in England
Where this data comes from
160 measurements from 1 monitoring station, 2016–2026. Retrieved from the Environment Agency (England; not the EPA Water Quality Portal) on 2026-08-16.
Collected and reported by
- Environment Agency (England)
ea-wqa160 samples · 2016–2026
Monitoring station identifiers (1)
NW-88010014
Authority classifications are stored separately from LakeQuality A–F letters and are never blended. See methodology and data sources.
Data Sources
Water quality data from the EPA Water Quality Portal
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2026-05-14
Monitoring stations: 1