I'd ask someone with the expertise. Probably toolmarks, but in any case, identification is not a matter of rating from 1 to 5 stars like on Amazon.
Wooden post© State Office for Heritage Management and Archaeology Saxony-Anhalt, Juraj Lipták
“According to initial findings, a post 1.60 meters (5.2 feet) high with felling marks and split boards up to 1.30 meters (4.3 feet) long could be remnants of architectural structures.”
https://phys.org/news/2026-09-wood-beneath-german-lake-reveal.html