When you visit Yakushima, I highly recommend spending a few hours kayaking in Anbo. You won't be disappointed. The water is amazingly clear, the scenery beautiful, and you may even be lucky enough to spot a flying fish or two (yes, you aren't going crazy if you think you see a fish jump out of the water)!
Although there are guided tours available, we were keen to just hire the kayaks and go exploring ourselves. We hired one man kayaks on the south side of the river, near the second bridge. They cost 3,000 yen each (life jacket included), and we were told we could use them for as long as we liked (although realistically the timing is limited, as there is a part of the river that you will come to and have to turn around, as there are too many rocks to kayak through). We ended up returning our kayaks after about 2.5 hours.
After jumping in the kayaks, we headed upstream. The river starts off quite wide and deep, but as you get further upstream, it narrows in places, and in some parts it's extremely shallow. The colours of the water and the rocks are stunning. Many times we stopped and just sat in our kayaks admiring the view and watching the fish swimming below us. It was so peaceful and relaxing. We also noticed that the banks were home to many, many crabs, which kept us entertained for a while as we watched them going in and out of their holes!
After about an hour of paddling on and off, we came to a section of rocks that looked impossible to pass. We got out of our kayaks and lifted them out of the water (remembering that it's a tidal river, so we didn't want the water level to rise and take our kayaks with it!) and went exploring over the rocks. The scenery was stunning. Eventually we got back in our kayaks and headed back to the start of the river.
After returning our kayaks we walked across the bridge to the north side off the river and ate lunch at "Ji ji ka", where they serve 'flying fish' burgers and the local udon (thick wheat-flour noodle). Both were great.