King County Freshwater Swim Beach Water Quality Observations

King County's Swim Beach program monitors temperature and bacteria levels at freshwater beaches, primarily on Lake Washington and Lake Sammamish. Each row represents a single observation, with data typically collected from mid-May to late September each year. The dataset tracks both current conditions and 30-day statistical summaries for public health and recreational safety.

Use Cases

• Issuing daily swim advisories using the HighToday flag and WaterTempF/C columns.
• Analyzing seasonal bacterial trends using the Geomean30d and nSamplesHigh30d columns.
• Comparing water quality across specific beaches using the Beach and Jurisdiction columns.
• Correlating bacterial levels with temperature over time using the Date, Time, and Sample A/B/C columns.

Strengths

• Provides a 30-day geometric mean (Geomean30d) for bacterial levels, offering a stable trend indicator.
• Includes three individual sample results (Sample A, Sample B, Sample C) alongside summary statistics.
• Data is collected regularly during a defined monitoring season (mid-May to late September).
• Available on multiple public platforms (Socrata, Data.gov), indicating official use and validation.

Limitations

• Key metadata like row count and file size is missing or conflicting across sources.
• The license is ambiguously specified as 'other-license-specified' with restrictive terms of use.
• Data is seasonal, limiting year-round analysis, and temporal coverage is not explicitly stated.

Provenance

Source

King County (data.kingcounty.gov)

Collection Method

Compiled by King County staff from a variety of sources as part of the Swim Beach monitoring program.

Time Range

Monitoring season from mid-May to late September annually.

Freshness

Last updated 2026-05-28 (Socrata), though this is a future date which may indicate a placeholder or error.

Geography

Freshwater beaches in King County, Washington, USA, specifically Lake Washington and Lake Sammamish.