It also has one of 60 tidal bores in the world (only 2 are in the United States, the other being the Knik Arm to the north of Anchorage). Tidal bores occur when the tidal water rises so rapidly that a wave front is created along the leading edge. The size of Turnagain's wave front can vary from day to day, ranging from 6 inches to 6 feet, and it travels about 10 miles per hour up the Arm.
So we read the brochures and websites, and found that a good place to watch the tidal bore come in was Bird Point. The bore would reach this site 2 hours and 15 minutes after low tide in Anchorage (3:18 P.M.), or about 5:33. The literature recommended we get there 1/2 hour early, because all the times were tentative.
We got there earlier than that, and spent some time talking to park volunteers -- one of whom had a Meade LX200 telescope trained on a black bear in the neighboring hills. We also got to see several bald eagles on the shore of the Arm as they grabbed some fish for dinner. By the time 5:15 rolled around, we had quite a nice group of fellow bore-watchers.
We kept scanning the water, softly talking amongst ourselves about the spectacle to come. Anticipation and excitement grew. 5:30 came and went. Cameras and binoculars were ready. 5:35, still nothing.
But wait... the story isn't actually over. Because the tidal bore travels about 10 miles an hour, it is quite easy to overtake it in a car, which we did. We saw a huge crowd at the next pull-off where the bore was just about to reach. So we stopped, and found what was to us a previously unknown sport -- bore surfing!
The white line of the bore was now closer to our vantage point and easier to see. The three small black dots on it are surfers: