Newcastle Beach Park is off-limits to swimmers for now, after county testing flagged the water as a potential health risk just as summer swim season ramps up.
On Wednesday, bright warning signs went up telling people to stay out of the water, and Bellevue Parks & Community Services quickly shared photos of the closure on social media. The city said the advisory came from Public Health — Seattle & King County and applies to the designated swimming area at Bellevue’s largest lakefront park, according to the City of Bellevue, Washington — Government on Facebook.
Public Health sets the rules for when beaches get flagged, and the bar is pretty clear: if multiple samples show bacteria levels above 320 colony-forming units (CFU) per 100 mL, or if 30-day averages climb too high, officials recommend that people and pets stay out of the water. Those criteria are laid out on King County’s lake swim beach page.
How county testing flags swim risks
The county’s testing routine is straightforward but strict. Staff collect three water samples at each swim beach and measure bacteria in CFU per 100 mL. If two or all three readings come in above 320 CFU, the beach is typically flagged as unsafe, according to local reporting.
That threshold has already triggered a few closures this month. Earlier spikes prompted temporary shutdowns at Madison Park, Gene Coulon, and Seward Park, a reminder of how quickly a seemingly calm lake can tip from “perfect swim day” to “better stay on the sand,” according to KIRO 7.
Where to check and how to stay safe
For anyone trying to dodge surprise closures, King County keeps an updated suite of tools online, including an interactive map, weekly test results, and optional email or text alerts so swimmers can confirm beach status before heading out. The county also urges people not to swallow lake water and to keep kids and pets away from any posted swim closures; details are listed on King County’s lake swim beach map, along with test dates and current advisories.
Bellevue Parks & Community Services says warning signs clearly mark the affected swim zone and that its social channels will be updated if conditions change. Anyone planning a trip to Newcastle Beach in the coming days is being urged to check official county and city updates and to avoid entering or touching the water until bacteria levels test back in the safe range.
