Stiles was struggling to run through the water but when he heard Derek splashing around behind him it pumped adrenaline right into his bloodstream. With a second wind Stiles got out of the river and started to run as fast and hard as he could away from Derek even though he knew it was pointless. He would be caught and Derek would punish him. Which brought on whole other thoughts. Thoughts that really didn't help Stiles run at all.