The Turnagain Arm bore tide was met by plenty of surfers, paddleboarders, and tailgating locals and tourists July 22-24. This wall of water comes in after extreme low tides created by the full or new moon. It occurs twice a day, around 11 hours apart. Bore tides are nature’s true “tidal waves” — occurring when an incoming tide builds into a large, dramatic front as it rushes into a narrow channel or river against the outgoing current. Turnagain Arm is the only place in the U.S. where the bores strike with regularity, although bores can churn up Knik Arm too.