So..I have 130 swimming.

I'm a paladin wearing some HP, LC and LP, but all my hinderance is trained down to insignificant. Despite that I cannot make it around the boulder in the middle of the river period while wearing my armor, having to remove it. I have no encumbrance or wounds.

This seems odd..im not encumbered (armor is not heavy to me) nor is it hindering me, but the difference is night and day. In fact I tried putting on some very hindering leather armor (i have no ranks in it) and I was able to swim around it just fine.

Theres seems to be something in swimming a bit hard coded to discriminate against metal armor, but if you have no encumbrance (i.e its not heavy) or hindrance, I do not see the reasoning for this.