Letter to Stew is a written note that can be found in Dishonored.
Hey Stew, here's the deal.
The old Greaves Refinery still has vats filled with processed whale oil that no one's touched. We just need to collect a bunch of empty tanks, and use the pumps they have at the front station to fill them back up. With the water level so high we'd be able to just pull a boat in and out, no problem. Just don't go alone. There's river krusts everywhere. Those critters are rough.