Deep Shadow by Randy Wayne White

Doc Ford and friends are back in a new thriller by Randy Wayne White. Doc, Tomlinson and Will Chaser are treasure hunting in a Florida lake when an underwater avalanche traps Tomlinson and Will with a limited supply of air. Doc works to rescue them while also battling two on-the-run convicts who want in on the treasure. Oh, and there may be a huge alligator or some other sort of lake-dwelling monster that wants to eat them all. It's great stuff!