A chain of evidence unearthed by Daniel Terdiman of CNET suggests that a massive, four-story structure floating on a barge off Treasure Island in San Francisco Bay is owned by Google and may be a floating data center.

No one knows for sure what the structure contains or who owns it, but the balance of the evidence suggests that it’s a real-world implementation of a floating data center first patented by Google in 2009.

Google Google’s original patent for a floating data center may be the prototype for the design currently floating in San Francisco bay.

There are a number of reasons Google might want to build a floating data center, including the ability to bring the massive computing power required to power Google’s search and other services as close to the places where it’s used as possible. Ocean water provides a natural source of coolant for a data center, and cooling is such a critical issue in data centers that companies like Facebook have started building them above the arctic circle.

We’ve contacted Google for comment.