Mount Baker Beach is off-limits for swimmers after routine water tests picked up elevated bacteria levels that could make people and pets sick, Seattle Parks and Recreation said Wednesday. Lifeguards and parks staff have lined the shoreline with warning signs while county health teams prepare follow-up sampling, with new test results still pending.
In a Facebook post, Seattle Parks & Recreation warned that the water at Mount Baker Beach "could make you sick" and pointed residents to county testing information for the latest numbers. The agency is asking visitors to skip swimming and wading, and to keep pets out of the lake, until health officials clear the beach to reopen.
What triggered the advisory
According to Public Health - Seattle & King County, the county typically advises people to "stay out of the water" when two or three samples collected the same day are above 320 colony-forming units (CFU) per 100 milliliters, or when the 30‑day geometric mean exceeds 100 CFU. County guidance notes that contaminated water can cause rashes, stomach upset, vomiting and infections of the eyes, ears or skin, and that children, older adults and people with weakened immune systems face higher risks of getting sick.
Not unusual during summer
Spikes in bacteria at swim beaches are a familiar warm-weather headache, often tied to storm runoff, failing sewer lines and wildlife. Officials typically retest multiple times before deciding a site is safe to reopen. A similar cluster of early-season closures hit King County in May, covered in a Hoodline post titled Bacteria Scare Shuts Down Three, as crews worked to track down contamination sources and update beach signage.
What beachgoers should do now
For now, the playbook is simple: stay out of the water, keep kids and dogs away from the shoreline and avoid swallowing any lake water until the swim area officially reopens. For retest schedules, current bacteria results and sign-ups for email or text alerts, visit King County's lake‑beach page. For lifeguard hours and local closure notices, check Seattle Parks' beach page.
