I am an industrial appraiser and this looks to me like a jacketed stainless steel tank, somewhere around 10,000 gallon capacity. I’ll bet somebody paid about $35,000 for this on the used market. They were probably shipping it by boat and it fell off. That would be my guess.
I would be suspicious about it though if nobody filed an insurance claim.
I went sailing once with an ex-girlfriend and when we finally arrived at the marina at the end of the day, I discovered she had fallen off the boat somewhere along the way................
That was my story and I'm sticking to it!