Wow thank you so much! I had fished in the spot you mentioned, but, between the waterfall and the bridge or on the other side of the big pillar. I found that if I went to where I couldn't see Claire, I got the fish! Then I tried fishing off of the bridge itself, so that the bobber was behind the pillar, and I eventually got the fish there too. Now I have the Golden Fishing Rod! (Where did you look it up? I didn't think a game this small would have a walkthrough or reference. :-)
It looks like the board up the waterfall is a section of one of the broken bridges from up higher and not a barrier to a tunnel.
I did find the other end of the icy passage too. Thanks for that! I might have found it eventually but it's easy to miss.
I have 20 golden feathers and 2 silver feathers. I found that having the bouncy flowers opened helps with the parkour race so I will keep at it. I think that and the flowers are all I need to finish in this game.
By the way did you find the little island with the girl selling sun hats? I had stumbled upon it early in the game but couldn't find it again for the longest time. It's offshore northeast from the boat.
Thanks again!