Volcanos in the park--Tim

I stopped by the park during my lunch break on Thursday, not many people there as usual. Stayed close to the truck while eating my lunch. Then I cleaned up some trash in the main lot; and chased a couple of snakes out of the trickle of water left running out from under the parking lot. I then went to the third parking lot and wandered around the remaining swampy water near the road. I have noticed a few times while at the park that there are little volcanos of mud near the edge of the water. Are they frogs? Are they crawdads? Does anyone know? Curiosity has gotten me,I might have to take a shovel next time.