Lake Thoreau
Fairfax County, Virginia40 acresView mapDirections
Virginia DEQ publishes the water-quality measurements for Lake Thoreau. Here is what has been measured.
- 43 ft max depth
- Limited data
Ask about Lake Thoreau
Answers come straight from the public measurements and survey records on this page.
Lake Thoreau in Fairfax County, Virginia has water-quality measurements published by Virginia DEQ, shown here as reported. Water clarity: 10 ft visibility. Surface area: 40 acres.
Stays via Stay22
Stays near Lake Thoreau
Compare lakeside cabins, hotels, and vacation rentals near Lake Thoreau in Fairfax County, Virginia — 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 Lake Thoreau
Prices for Sep 18–20, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Virginia’s top lakes →
Follow Lake Thoreau’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Lake Thoreau is a 40-acre lake in Fairfax County, Virginia with an estimated average depth of about 43 feet. Overall water quality is improving over recent sampling years.
Source: EPA Water Quality Portal sampling records, Virginia DEQ, last sampled 2022-07-11. Grade methodology: LakeQuality methodology.
What Lake Thoreau is good for
From access and monitoring records, not editorial picks.
- Clear water10 ft of visibility
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Lake Thoreau 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 Lake Thoreau
These are the measurements Virginia DEQ publishes for Lake Thoreau, 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 10 ft. TSI 44.
| Metric | Value | EPA condition class |
|---|---|---|
| Water Clarity (Secchi Depth) | 10 ft | Measured, not scored |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~43 ft est. |
| Average Depth | ~9 ft est. |
| Surface Area | 40 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Virginia has not published bathymetry for Lake Thoreau.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Lake Thoreau
Water Quality Trend: ↑ Improving
Based on 10 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +2.578 m/yr | 10 |
Reservoir Info (USACE NID)
Lake Thoreau is a man-made reservoir impounded by the Lake Thoreau Dam, built primarily for recreation on the TR-Snakeden Branch; earth-type dam, 56 ft tall and 850 ft long.
- Surface area
- 40 ac
- Normal storage
- 813 ac-ft
- Max storage
- 1,406 ac-ft
- Drainage area
- 0.6 sq mi
- Hazard class
- High
- Owner
- Reston Association;Reston Association
All listed purposes: Recreation;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID VA059013 · Operator website
Nearby Lakes in Fairfax County
Frequently asked questions about Lake Thoreau
Where is Lake Thoreau?
- Lake Thoreau is a lake in Fairfax County, Virginia. Its water-quality measurements are published by Virginia DEQ and shown on this page as reported.
What is the water quality of Lake Thoreau?
- Lake Thoreau in Fairfax County, Virginia has water-quality measurements published by Virginia DEQ, shown here as reported. Water clarity: 10 ft visibility. Surface area: 40 acres.
Is Lake Thoreau safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Lake Thoreau?
- No published bathymetric survey covers Lake Thoreau, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 43 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 40 acres.
Explore Lake Thoreau across LakeQuality
More lakes in Virginia
Other Lakes in Virginia
Mesotrophic Lakes in Virginia
Where this data comes from
3 measurements from 1 monitoring station, 2019–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS3 samples · 2019–2022
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
Lake size & watershed from HydroLAKES (HydroSHEDS)