Derwent Water
Cumbria and Lancashire, EnglandView mapDirections
EA publishes the water-quality measurements for Derwent Water. Here is what has been measured.
- Limited data
Derwent Water in Cumbria and Lancashire, England has official water-quality measurements, shown as reported. Phosphorus: 11 µg/L. Chlorophyll-a (algae): 2.7 µg/L.
How Derwent Water is classified
Derwent Water in England is published with the authority's own measurements and class. The measurements here are published by the agency that samples the lake, as reported. Sampling here has recorded phosphorus and algae (chlorophyll-a), but not water clarity.
LakeQuality publishes no grade of its own beside it. Everything below thathas been measured is reported on this page.
Monitoring: the Environment Agency (England).
Derwent Water is a lake in Cumbria and Lancashire County, England.
Source: the Environment Agency (England) — not the EPA Water Quality Portal, last sampled 2026-03-18. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Derwent Water is safe to swim in today is a call for the Environment Agency (England) and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Derwent Water
These are the measurements EA publishes for Derwent Water. More on the source.
No clarity data. Phosphorus 11 µg/L. Chlorophyll-a 2.7 µg/L. TSI 39.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 11µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 2.7µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 39 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
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Answers come straight from the public measurements and survey records on this page.
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Frequently asked questions about Derwent Water
Where is Derwent Water?
- Derwent Water is a lake in Cumbria and Lancashire, England. This page reports official water-quality measurements, shown as reported.
What is the water quality of Derwent Water?
- Derwent Water in Cumbria and Lancashire, England has official water-quality measurements, shown as reported. Phosphorus: 11 µg/L. Chlorophyll-a (algae): 2.7 µg/L.
Is Derwent Water safe to swim in?
- Derwent Water 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.
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Where this data comes from
11 measurements from 1 monitoring station, 2025–2026. Retrieved from the Environment Agency (England; not the EPA Water Quality Portal) on 2026-08-16.
Collected and reported by
- Environment Agency (England)
ea-wqa11 samples · 2025–2026
Monitoring station identifiers (1)
NW-LSN112
Authority classifications are shown as the authority published them. See where the data comes from and data sources.