Vampire casts Swim - what happens?

[Ettina]

So, vampires can't handle running water, unless the base creature has a swim speed. But what happens if a vampire of some race that can't normally swim gains a swim speed, such as using the spell Swim or donning an item that grants the ability to swim?

[Necroticplague]

The base creature still doesn't have a swim speed (since it no longer exists to be buffed), so the vampire is still vulnerable to running water. On the other hand, if you temporarily buff yourself with a swim speed, and are vamped while that effect is active, you remain immune to running water even after the spell wears off (since all things about templates only apply at the moment the template is added, unlike PRCs or feats).

[Hecuba]

The base creature is the creature that the character was before the application of the vampire template.