Lake Sammamish
King County, WashingtonView mapDirections
Not Rated: one monitoring station are on record, but they measured water clarity only. LakeQuality’s A–F method grades total phosphorus, total nitrogen, chlorophyll-a, and turbidity; clarity is shown, not scored.
- Impaired · Mercury
- 320 ft max depth
- Public access
- Limited data
Lake Sammamish in King County, Washington is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 11.5 ft visibility.
- Clarity
- 11.5 ft
- Max depth
- ~320 ft est.
- Trend
- → Stable
- Public access
- Yes
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Watch Lake Sammamish’s letter
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Why Lake Sammamish has no grade
Lake Sammamish has monitoring on record from one station, but only water clarity was measured. LakeQuality’s A–F letter uses total phosphorus, total nitrogen, chlorophyll-a, and turbidity against EPA National Lakes Assessment condition classes. With none of those grading measurements on record, Lake Sammamish is Not Rated — not an F. Its 11.5-foot median from 6 readings collected 2012–2021 is still shown as clarity, but clarity alone cannot earn a letter.
Not Rated is EPA Integrated Reporting Category 3 — insufficient information. Everything below that has been measured is still reported on this page.
Sampling is run by WA Ecology and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Lake Sammamish is a lake in King County, Washington with an estimated average depth of about 320 feet. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, WA Ecology, last sampled 2021-07-06. Grade methodology: LakeQuality methodology.
What Lake Sammamish is good for
From access and monitoring records, not editorial picks.
- Clear water11.5 ft of visibility
- Boat launch1 documented ramp
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Lake Sammamish is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pCBs. Check local advisories before you swim.
Water quality measurements for Lake Sammamish
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 11.5 ft. TSI 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~320 ft est. |
| Average Depth | ~83 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Washington has not published bathymetry for Lake Sammamish.
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.
Recreation & Access
- Lake Sammamish State ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake Sammamish
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.031 m/yr | 6 |
EPA Impairment Status
Lake Sammamish is officially listed as impaired under Clean Water Act §303(d) in the 2018 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WA47122G0A9_01_01 · Official waterbody report
Nearby Lakes in King County
Frequently asked questions about Lake Sammamish
Where is Lake Sammamish?
- Lake Sammamish is a lake in King County, Washington. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Lake Sammamish?
- Lake Sammamish in King County, Washington is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 11.5 ft visibility.
Is Lake Sammamish safe to swim in?
- The letter is not a swimming clearance. Lake Sammamish is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pCBs. Check local advisories before you swim.
How deep is Lake Sammamish?
- No published bathymetric survey covers Lake Sammamish, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 320 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Lake Sammamish?
- Lake Sammamish has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lake Sammamish State Park. Public access is listed as yes.
Explore Lake Sammamish across LakeQuality
Depth, room, public access, and the state wake-sport rules
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Where this data comes from
6 measurements from 1 monitoring station, 2012–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS6 samples · 2012–2021
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory