An 80 gram lead is quite a chunk - I use something like that when bottom fishing. The round shape speaks against it, however, and leads rolling on the bottom of the water are rather undesirable when fishing. Perhaps a lead from a fishing net or from textile processing.
Niedersachse 6.1.2024
That could be the case, and the lead is probably not that old. The bodies of water near the site do not exist on a map from the 19th century.