He could have a thorn or other sharp object imbedded in his foot, causing pain when he walks. (cuteness.com)
Taking care to be mindful of the surfaces your dog is walking over is important, however even when you're watchful it's still possible for your pooch to walk over glass or other sharp objects which could lacerate their paws or pads. (mypetneedsthat.com)
If the creek has a sandy bottom, you can take the shoes off so he can explore without, but it is best to be prepared since most creeks have lots of rocks and other sharp objects that can hurt tender little feet. (natural-parenting-advice.com)