This one is a bit tricky. There is more than one solution, but the all follow a similar pattern.

Think about this: while the wolf is faster than you in a straight run, you can have a faster angular velocity than the wolf if you set it up correctly. Swim a few feet away from the center of the lake and begin to swim in circles around the center. Because you are closer to the center than the wolf, your angular velocity is much quicker. By swimming out to just less than radius/4, you can continue to swim in circles quicker than the wolf. If you continue to swim the wolf will begin to lag further and further behind. Eventually, the wolf will be directly across from you and you can swim directly to the nearest shore and make it before the wolf.