Mudlarks will dig through rivers, looking for valuables. Mudlarks require 1 gold per day to dredge. They have a 10% chance of finding an item in a lake or river, +1% per day they have been searching. After 30 days, there is no more chance of recovering items. If a mudlark is looking for a particular item, there is a 50% chance item found is that item. Otherwise, it is a random item from the DMG.
Sewer hunters, mudlarks that work in toxic banks, require 5 gold per day.