I got mine up to max in about an hour and a half a couple months ago by manually holding down forward+left in North Ro.

Didn't ever get a single skill up when I tried to num lock it.

I haven't seen this mentioned, but are you level 40+? Swimming skill caps out at something like (level * 5).

What I have always done on P99 is to autorun while swimming with the left ot ight arrow key held sown so I swim in tight circles. I think the key is to be doing something other than looking right at the screen--it is agonizingly slow.

It's been mentioned already but I wanted to rephrase it as clearly as possible:

Swimming will not skill up by just pressing auto-run against a wall while in water.

The chances of a skill-up are dependent on the character changing position in the zone (/loc ). There are all sorts of clever ways to have your character jostle about while afk.

I think the Timorus Deep firepots are a good way to both help and encourage players to raise their swimming. It's never wasted time going there because of the obvious time-saving potential of the firepots, and the length of the swim will quickly get you to (200) after only a few trips.

Also, I've found my characters with higher intelligence seem to increase swim skill faster and more often.

Did the auto-circle trick in Felwithe this morning to see how fast it went up, just out of curiosity. At 135 WIS and 126 swimming, it took a few hours but it wasn't as bad as the last time I attempted to skill up. Here are my timestamps:

I tried using levitate first, but it was hard to keep my feet in the water and with Scale of Wolf I went ridiculously fast for no reason since I wasn't going anywhere.

Can confirm that swimming skill is time consuming to skillup. Usually 5-6 hours for 1-200.

On live 1-400 took 18!!!! Hours.

Another place to skill up swimming is in Innothule Swamp. Try the northeast corner. Just run in a circle in the shallow part for a few hours.

Go classic and swim in a circle in East Freeport, down by the docks...

Oh god this works like gangbusters.
Skill is going up like there's no tomorrow.

http://imgur.com/a/JBF6h

Forgive the crappy screenshots. Just wanted to give some proof that swimming, at least against some walls, still works. If it is based off of your /loc changing, it doesn't need to change very much.