It is actually not a condition, but a natural process. As you know, fingers and toes wrinkle naturally when immersed because as you take on water because the top layer swells, but it is superficial. The under-layer does not plump cuasing the wrinkled look on top. When your body is immersed, your skin which is actually one very large organ, takes on water which spreads throughout the cells of the skin, including those that are not immersed. The same process causes the skin on the fingers to look wrinkled. As long as they return to normal, as the rest of your skin does after drying, there is no cause for concern.
I haven't found a specific web site referencing this exact explanation, but the above references explains the wrinkling process and the skin's properties, which I think will lay it out for you.
Do your fingers stay wrinkled, or is it something that happens occasionally?
The reason that fingers wrinkle like this, as mentioned by Christy, is due to water or moisture on the skin that absorbs into the top layer, but not the bottom. Since the two layers are attached (sort of glued together), they prune.
It's best known for happening after you get out of the pool or a long shower, but other reasons it might happen is if you're in a particularly humid environment, or especially if you tend to have sweaty hands from time to time. Some people have excessive sweating in some areas of their body and not others (called hyperhidrosis), which can involve the hands.
I hope this helps!