Highway 101 Bridge, Mud Bay is a freshwater beach in Thurston County, Washington. Across 127 bacteria samples collected between 2021 and 2026 at nearby monitoring stations, it earns a Beach Safety Grade of C — Fair.
About 11% of samples at Highway 101 Bridge, Mud Bay 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 sometimes crossed here over the monitored period. Bacteria samples occasionally exceed the safe-swimming threshold — check the latest advisory before swimming.
Highway 101 Bridge, Mud 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.