Potlatch State Park Tidelands is a saltwater beach in Mason County, Washington. Across 501 bacteria samples collected between 2021 and 2025 at nearby monitoring stations, it earns a Beach Safety Grade of B — Good.
About 4% of samples at Potlatch State Park Tidelands exceeded the EPA Beach Action Value of 235 CFU/100 mL for Escherichia coli — 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 rarely exceed the safe-swimming threshold.
The evidence behind this grade is deep for a beach page: 501 results from 34 monitoring stations, spanning 2021 to 2025. Enough sampling, from enough places, over enough seasons that one bad week can't drive the letter.
Potlatch State Park Tidelands 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.