The Wailua is the signature river on Kauai. It’s the home of Smith’s Luau and the Fern Grotto. There is also an historic Hawaiian village you can visit. But the best way to see the Wailua is by kayak or paddle board. You can rent boards and kayaks at the mouth of the river at Kayak Kauai or at the Hawaiian village.
The most important thing to watch out for on the Wailua is the wind. Pay attention to the forecast. If the winds are above 12mph I’d be careful. Best time to go is early in the morning before the winds come up. They are can blow you upstream or downstream and can get pretty strong.
If the winds are coming downstream I’d suggest renting at the mouth and see how far up you can get. Getting back will be easy. If the winds seem to be going upstream then you can rent at the Hawaiian Village and get as far down as you can.
But if you have calm winds I suggest putting in to the north of the bridge. Turn left at the first road past the bridge and watch out for the signs to a small park. There is a perfect put in spot there, as long as there aren’t boats speeding around.
Go upriver and you’ll pass the Hawaiian Village. You can turn to the left fork and go to the Fern Grotto dock but it’s not really conducive to paddle boards or kayaks. There is a small place to the right where you could tie up and climb to shore. The Fern Grotto is worth it.
Continue up that left fork and the stream narrows and gets shallow but is worth it. Come back down and take the right fork and there is a trail to Secret Falls. Don’t go if it’s been raining as it’s just a muddy slog. You even have to cross a stream by holding onto a rope. But it is a fun trip.