I'm past the Bronze dragon, but can't get past the river...

How do I explore the Spire? (I see the hole to the floor above, but can't get there...)

Thanks in advance for any advice.

SG

Ensure you enter the river at the upstream point (south landing) and let the current carry you north. Swim over to the east wall and hug it until you see an east landing. Run-jump onto it (it can be tricky).

If you go past you'll end up on the north river landing. Head back to the south landing via the tunnel and try again.

Just persevere. First, walk along the edge of the river (in the direction you can't swim) as far as you can go, then jump in and start swimming against the stream. If you keep trying to swim against the current, shifting left and right against the game's attempts to spin you back the other way, you will eventually get to the wall of water (a W&W waterfall?) and be able to pass through it to a small wooden platform with a ladder going up.