This impressive structure was put up by beavers in the past few weeks. Beavers are making a huge comeback in the waterways around here. They are active mostly at night, so you don't see them - just their handiwork and the trees they knock down.
It always surprises me how quickly they can construct one of these. I've only caught one once carrying a twig in his teeth while swimming. The Corps fights these guys continually as the dam up the creeks in the park :)
