Oregon

Oregon's tidal coast runs from the Columbia River mouth at Astoria south past Tillamook, Newport, and Coos Bay to the California border at Brookings. The tide here is the open-Pacific mixed-semidiurnal signal that the entire west coast shares — two highs and two lows of unequal size each day, the bigger swing falling on the lower-low water — modulated by river-mouth geometry along a coast that has more major estuaries per kilometre than any other US state. Mean range at Astoria is about 2.4 metres, climbing past 2.9 on spring tides. Down the coast at Newport's Yaquina Bay and Coos Bay the range is similar but the bar geometry differs at each entrance, and the pilots who work the shipping channels at the Columbia and at Coos Bay maintain real-time current and swell information that is the authoritative source for crossing decisions. The lowest spring lows of the month open the rocky intertidal at Cannon Beach, Cape Perpetua, and Yachats — among the better tidepool zones on the US west coast. Pacific storm surge in winter can lift water levels 20–30 cm above predicted; harmonic predictions assume calm.