My chocolate lab, pit bull mix is a weirdo. First of all she does not like water. She doesn't like baths, rain, puddles, etc. But if we're at the creek or river she'll reluctantly get in if we go downstream because she doesn't want to be alone. But first chance she gets when we become stagnant she will get on dry land.
The funny thing is though that she will watch the water for sticks - whether they are drifting by or submerged in place in the water - and then go after them. I mean she hates water but she'll dunk her head underneath it and struggle to get the stick out until the job is done. Then she'll take the sticks one by one and go far away and pile them up. She doesn't bring them to anybody - she hates fetch in fact - she takes them away from everybody. Once I watched as she pulled a stick that was way taller than me (I'm 5' 9") and thicker than my wrist up a pretty big sandy hill (our sand is really fine beach sand). And she was only 35 pounds at the time.
What in the world could possibly be in her head to do this? It's nothing I've read or heard about a dog doing. The closest I've come is that labs are hunters and it's ingrained in them to hunt stuff and bring it to their masters. That's sort of what she does but way different at the same time. Because if I go near her pile she starts running circles around me as if to distract me from them.
All I can tell you is 'Stick Fetish' is not unusual. Gracie is nuts about pulling submerged limbs. How old is your girl ?