From the pictures the tooth looks to be a human maxillary premolar. The enamel on the crown has not be degraded. (It is the hardest substance in the body) The root of the tooth is covered by cementum which appears to be worn. (Probably from a long time in the water)
It looks like someone lost this tooth some time ago atraumatically. Most teeth lost by trauma in the posterior mouth are fractured and not whole. Sorry no fossil.
I have a lot of experience with dental trauma and teeth as an Oral and Maxillofacial Surgeon.
Wow! You just never know who might be reading your post on the internet. Good stuff!