The Fathom Line is a crew of eighteen divers and underwater demolition specialists who control access to the submerged sections of Milwaukee's old port infrastructure. When lake levels shifted and the harbor district partially flooded, an entire layer of the city went underwater — warehouses, transit tunnels, industrial facilities, and the sealed vaults of businesses that didn't have time to relocate their assets. The Fathom Line makes its living accessing these submerged spaces and extracting what's inside.

Unlike the Lakebed Scrapers in Chicago, who focus on volume salvage, the Fathom Line specializes in precision recovery. They're hired by clients who know that something specific is down there — a sealed data vault, a flooded pharmaceutical stockpile, a cargo container that sank before it could be loaded — and need someone with the equipment and skills to retrieve it. The crew charges by the job, and their rates reflect the danger: cold water, zero visibility, unstable structures, and the constant risk of entrapment in a flooded space where rescue is impossible.

The crew's equipment is a mix of salvaged commercial diving gear, modified industrial tools, and custom-built underwater cutting and welding rigs. Several members run aquatic augments — gill-assist implants that extend dive time, pressure-resistant subdermal reinforcement, and sonar packages that let them navigate in total darkness. These augments are expensive to maintain, which keeps the crew perpetually working to fund their next round of modifications.

The Fathom Line also runs a sideline in underwater disposal. Need something to disappear permanently? The flooded harbor district has thousands of spaces that nobody will ever search. Bodies, evidence, weapons, data — the Fathom Line will sink it for a fee and guarantee it stays sunk.