The P&R covered bridge was long enough (~200 feet) that it had a center pier in the middle of the river that has since disappeared. The granite abutments are still in place on either side though.
The center pier didn't so much disappear as fell over into the river when there was some bad ice in it. Some of it is still there under the water but it's probably not salvageable at this point I would think. The center rock makes a great place to hang in the middle of the river when the water's low, though.