river rat

noun3

1. •
   A rat that lives on or along a river.
2. •
   (offensive) A lower-class person living on or along a river.

   • The river rat he fought was one of a gang of them lolling under the eaves of the porthouse, probably waiting for a gaming house to open. — 1989
3. •
   (disapproving) A poker player that wins a Texas Hold'em hand by making the winning hand on the river card.