This is a video taken by a drone capturing a Bore Tide in Turnagain Arm on Sep 15th this year, a few miles South of Anchorage.
The tides in Cook Inlet around this area are tremendous - up to 27 feet difference from low tide to high tide. It can reach up to 10 feet in height and travel about 15 MPH. Naturally, surfers love playing out in the Inlet when it comes, even though the water is very cold. The dirty color is from all the glaciers feeding into this area with their silt & sediment.
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I had a funny experience with a Bore Tide last Summer while fishing, with a bunch of canoes and kayaks all around getting dumped when it struck... seems to me I shared that story here, I'll link it if I did.