John Flannagan Reservoir
Dickenson County, VirginiaView mapDirections
Virginia DEQ publishes the water-quality measurements for John Flannagan Reservoir. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- Limited data
John Flannagan Reservoir in Dickenson County, Virginia has water-quality measurements published by Virginia DEQ, shown here as reported. Water clarity: 13.1 ft visibility. Phosphorus: 10 µg/L. Chlorophyll-a (algae): 1.5 µg/L.
John Flannagan Reservoir is a cold, clear oligotrophic lake in Dickenson County, Virginia. Overall water quality is improving over recent sampling years. Compared to the 3 other monitored lakes in Dickenson County, John Flannagan Reservoir ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Virginia DEQ, last sampled 2026-06-24. Methodology: how these readings are compared.
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What John Flannagan Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water13.1 ft of visibility
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. John Flannagan Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, oxygen depletion (low DO). Check local advisories before you swim.
Whether John Flannagan Reservoir is safe to swim in today is a call for the Virginia Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for John Flannagan Reservoir
These are the measurements Virginia DEQ publishes for John Flannagan Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13.1 ft. Phosphorus 10 µg/L. Chlorophyll-a 1.5 µg/L. TSI 37.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 10µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.5µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 37 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about John Flannagan Reservoir
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Fishing John Flannagan Reservoir
Water quality readings over time
2 seasons of samples on record (2025–2026). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
EPA Impairment Status
John Flannagan Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life, Fish consumption.
Source: EPA ATTAINS assessment unit VAS-Q13L_PNR01A02 · Official waterbody report
Nearby Lakes in Dickenson County
Frequently asked questions about John Flannagan Reservoir
Where is John Flannagan Reservoir?
- John Flannagan Reservoir is a lake in Dickenson County, Virginia. Its water-quality measurements are published by Virginia DEQ and shown on this page as reported.
What is the water quality of John Flannagan Reservoir?
- John Flannagan Reservoir in Dickenson County, Virginia has water-quality measurements published by Virginia DEQ, shown here as reported. Water clarity: 13.1 ft visibility. Phosphorus: 10 µg/L. Chlorophyll-a (algae): 1.5 µg/L.
Is John Flannagan Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. John Flannagan Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, oxygen depletion (low DO). Check local advisories before you swim.
Explore John Flannagan Reservoir across LakeQuality
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Where this data comes from
37 measurements from 1 monitoring station, 2025–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- VIRGINIA DEPARTMENT OF ENVIRONMENTAL QUALITY
21VASWCB37 samples · 2025–2026
Analytical methods
- Tyler, John. 1968. The secchi disk, Limnology and Oceanograpy, 13(1):1-6.
- Total Phosphorus After Block Digestion
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 446.0 ~ EPA; Chlorophylls and Pheopigments in Phytoplankton by Spectrophotometry
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database