Graham Payne, 69, from Birchills, Walsall, discovered the rare round-bottomed bottle at the bottom of the river, between the English and Welsh bridge in Shrewsbury.
Mr Payne's investigations into the history of the bottle led him to discover that it was made in the town.
He believes it may be of some financial value to a collector but plans to keep it for himself.
He said: "It is a real one of a kind, hand-crafted and made long before they started to make bottles with a flat bottom.
"I saw it at the bottom of the River Severn and had to bring it back up with me for a better look. Who knows how it got there?
"I brought it back up and is still in good condition, so since then I have been trying to find out more but it isn't easy. It could have real value to a collector but I am having it for myself as a keepsake. I am sure I can find somewhere for it."
Mr Payne says he has found valuables in the past, but never anything like this.
He said: "It is really unique, even in scuba diving, where you are finding things all the time. I have been scuba diving for around 30 years now and I have found lots in my time, mainly ammunition, but nothing like this."
This isn't the only instance of Mr Payne diving into the past. He has also helped dozens of people find out more about their parents, estranged relatives and family members who were involved in the First and Second World Wars, after being inspired at his local library.
Graham's previous research has also taken him further afield and seen him travel to Ypres in Belgium to find the graves of soldiers who died there in 1915.