Yep, there is indeed something on top of the cowling, maybe someone will know what it is.
There's a lump of wood in the water on the other side of the pier, in the high-res version it looks like a sleeper or something.
The periscope is in fact the top of the mast of a yacht moored in the foreground, out of frame.
As far as floating crap goes, a few logs here and there is nothing compared to dodging bigger floaties like tankers, yachts and countless Beavers and Otters - mind you, at least you can see them!