You may want to call the police department having jurisdiction over that area if the rightful owner has called it in as missing. We found one on the Folly not too long ago and were able to return it to it’s owner as a result of the kayak reported as missing having been reported to the police.
That’s exactly what happened with the one we found on the Folly - kayak got away from the fella’s dock… He was quite thankful we called the police as he’d just reported it missing not too long before we called.