Muddy Creek is a tributary of the Susquehanna River in York County, Pennsylvania, in the United States. Muddy Creek, formed by the confluence of the 11.2-mile-long North Branch and the 10.3-mile-long South Branch at the community of Muddy Creek Forks, flows for 17.2 miles to join the Susquehanna River in the backwater of Conowingo …Muddy Creek is a tributary of the Susquehanna River in York County, Pennsylvania, in the United States. Muddy Creek, formed by the confluence of the 11.2-mile-long North Branch and the 10.3-mile-long South Branch at the community of Muddy Creek Forks, flows for 17.2 miles to join the Susquehanna River in the backwater of Conowingo Reservoir.