South Fork Tolt Reservoir water level — Washington
South Fork Tolt Reservoir in Washington was last measured at 1,735.96 ft (datum NGVD29), as of Aug 31, 2026, 12:00 AM (UTC-07:00) (USGS Water Services). Over its recent trend window the level has been falling (−10.2 ft). This reading is provisional and subject to revision.
- % of conservation pool full
- Not reported
- Storage
- Not reported
- Recent trend
- ↓Falling
−10.2 ft over the trend window
Recent trend
Readings this station published between Jun 2, 2026 and Aug 31, 2026 — a 89-day window — downsampled for display.
Data: USGS Water Services (waterservices.usgs.gov) and USACE CWMS Data (cwms-data.usace.army.mil), retrieved 2026-08-31. Both public domain (a work of the U.S. Government, 17 U.S.C. §105).
Source: USGS site 12147900, retrieved Aug 31, 2026, 8:24 AM (UTC+00:00). Official page for this lake →
About this gauge's record
This site's drainage basin covers approximately 19 sq mi of contributing watershed.
The dam behind South Fork Tolt Reservoir
South Fork Tolt Reservoir is held back by Tolt River - South Fork (also recorded as Tolt Main Dam) , an earthfill embankment, holding the pool back by sheer mass and an impervious core rather than by the strength of concrete , standing 200 ft high and running 980 ft along its crest , built across South Fork Tolt River in King County , near Carnation . It was completed in 1962 , and is owned by City of Seattle (a local government owner) , to a design credited to Carey & Kramer Consulting Engineers.
Its recorded primary purpose is water supply — delivering water to its customers comes first, so drawdown here follows demand as much as it follows rainfall . It also serves water supply;hydroelectric.
It is founded on soil, with a earth core. Its spillway is ungated: once the pool reaches the crest, water leaves on its own and the operator cannot hold it back. Its outlet works use other controlled1.
NID classes it high hazard potential. That describes what a failure would cost downstream — loss of life would be expected — and says nothing about how likely a failure is, or what condition the dam is in. Its most recent condition assessment was fair: sound under normal loading, though a rare or extreme event could expose a deficiency. That assessment is dated 04/11/2023.
At its normal pool the reservoir covers about 1,040 acres. NID records a maximum storage of 68,400 acre-ft against a normal storage of 57,500 acre-ft. Its maximum discharge capacity is 13,000 cubic feet per second.
Dam facts: National Inventory of Dams record WA00177 , filed by Federal Energy Regulatory Commission — U.S. Army Corps of Engineers, public domain. Water levels above come from USGS Water Services and are a separate source. (How this dam was matched to this gauge →)
How South Fork Tolt Reservoir compares nearby
5 of 6 nearby lakes with a current trend are also falling right now.
Nearby lakes
The six nearest published lakes by centroid distance (great-circle) — cross-state neighbors included.
| Lake | State | Level | Distance |
|---|---|---|---|
| Spada Lake | WA | 1,425.95 ft | 31 km |
| Sammamish Lake | WA | 25.72 ft | 34 km |
| Howard a Hanson Reservoir | WA | 1,153.37 ft | 47 km |
| Lake Tapps | WA | 540.91 ft | 63 km |
| Mud Mountain Lake | WA | 917.85 ft | 64 km |
| Lake Shannon at Concrete | WA | 410.53 ft | 95 km |
Frequently asked questions
- What is the current water level of South Fork Tolt Reservoir?
- As of Aug 31, 2026, 12:00 AM (UTC-07:00), the pool elevation was 1,735.96 ft (datum NGVD29), provisional and subject to revision. See the trend chart above for the recent direction.
- Is South Fork Tolt Reservoir full right now?
- Its managing agency does not publish a %-of-conservation-pool-full figure for this lake, so we show the bare level rather than estimate one.
- Where does this data come from?
- From USGS site 12147900, retrieved Aug 31, 2026, 8:24 AM (UTC+00:00).
More in Washington
See every lake tracked in Washington, or read the methodology behind these figures.