I know it's a long shot, but I figured I'd give it a try.
My wife and I visited Kauai 20 years or so ago. On that trip, we visited a north-shore beach that, for some reason, I'd like to find again. As I recall, there was a stream that entered the beach on the left side, and a large tree with a rope that enabled you to swing out and drop off into the brackish water where the stream entered the beach. It wasn't very populated on a weekday in late August or early September. And I remember kayaking on that trip, though I can't be sure of the stream was the one we kayaked in or not.
And, though I'm absolutely sure this won't provide any help, I'll throw it in anyway: There was a dog there whose sole mission in life appeared to be fetching a stick thrown on the beach or in the water. I swear, his eyes never left the stick; he didn't respond to any petting, calls, or anything, only the stick.
Does any of this ring a bell with anyone?