Dive into adventure with Ars Natatoris! This brief and free product presents swimming and drowning rules compatible with a wide range of OSR games.
Says Megan R., Featured Reviewer, "Despite disclaimers about going for playability rather than realism, this has captured most of the niceties of aquatic exploits quite well, and unless you have a troop of Navy SEALs for a party should cover at least casual waterborne activities as an addendum to your chosen ruleset."
Now at Paizo.com:
Dive into adventure with Ars Natatoris! This brief product presents swimming and drowning rules compatible with a wide range of old-school games.