East Beach County Park, Mystery Bay is a saltwater beach in Jefferson County, Washington. Across 55 bacteria samples collected between 2022 and 2023 at nearby monitoring stations, it earns a Beach Safety Grade of A — Excellent.
About 2% of samples at East Beach County Park, Mystery Bay exceeded the EPA Beach Action Value of 104 CFU/100 mL for Enterococcus — the threshold at which water managers typically post a swimming advisory. In practice that means the safe-swimming limit was rarely crossed here over the monitored period. Bacteria samples almost never exceed the safe-swimming threshold.
East Beach County Park, Mystery Bay was not under a swimming advisory in the most recent EPA snapshot. Conditions can change quickly after heavy rain or high runoff, so it's still worth checking the current advisory the day you go.