What was that thing by the old Arrowhead Bridge?

I don't see it in this photo, but maybe it was out of camera range.

Should I have asked "what is that thing" or was I right to have asked "what was that thing"?

According to Matt Hannula, the object in question is a channel marker. "According to the NOAA chart, it flashes green at a 4 second interval, and appears to be right on the boundary of the navigable channel," he writes.





Gene Rebeck writes, "I don't know what it is or what it's for, but based on Google Maps' aerial view, it appears to be still there. Not a figment of distant cousin's imagination."

Yes! Well that was quick. Thanks Distant Cousin.
(Start chant now ... distant, distant, distant...)

I do remember that.  I liked to think it was an underwater lab as a kid.

Bing's birdseye view has a closer shot of it. 

Looks like a piling similar to the 4 you see below the span on the Bong Bridge.

It's definitely still there. My theory is that ships passing through the narrow opening of the railroad swing bridge line up their steering pole with this object. This helps to ensure they pass straight through the bridge opening. Checking the aerial photo, it appears to be perfectly in line with the course a ship would take going through the bridge. There also appears to be a solar panel on the object, which I believe may power a light so the object can be seen at night. That's my theory, at least.