The Dyvisive Deep (2006)

A One-Round Living Greyhawk Dyvers Regional Adventure

From the introduction:

Six weeks ago, a group of wide-eyed sailors was fished out of the Nyr Dyv telling tales of terrible beasts of the lake rising up and rending their ship to splinters. Since then, more sailors have been fished from the lake with equally fantastic tales, some even claiming the lake itself was striking against them. It is no surprise then when Guildmaster Nathas of the Dyvers Adventurer’s Guild posts a job for a group of adventurers to guard a ship bound for Safeton. The only questions are whether the lake really does have a mind of its own, and if so, are you brave (or greedy) enough to confront it?

A Dyvers waterborne regional adventure and part two of the Machinations Saga for [character levels] 2 - 12.

Membership in the Dyvers Adventurer’s Guild is highly recommended.