river rat
/ˈrɪvə rat/noun
1A rat or any of various other rodents living on or near rivers.
2 North American slang. A person engaging in criminal activities on a river; a river thief or river pirate. Now chiefly historical.
3 North American slang. A person who works lives or works on a river.
4Specifically = river-driver. Compare river hog. Now rare.
Origin
Early 18th century; earliest use found in Aaron Hill (1685–1750), writer and entrepreneur. From river + rat.