Oatka Creek ( ) is the third longest tributary of the Genesee River, located entirely in the Western New York region of the U.S. state of New York. From southern Wyoming County, it flows to the Genesee near Scottsville, draining an area of that includes all or part of 23 towns and villages in Wyoming, Genesee, Livingston and Monroe counties as well. Its name means "leaving the highlands" or "approaching an opening" in Seneca. Like its parent stream it originated during the end of the last Ice Age, as glacial impact on the upper Allegheny Plateau created a rolling landscape streams could gradually erode through, The Oatka carved a deep groove known today as the Oatka Valley, where the upper creek's two major settlements would be established. Native Americans of the Seneca nation established a few settlements along it where clearings arose in the forest. The Revolutionary War's Sullivan Expedition, brought the valley's fertile soil to the attention of the emerging nation, and the region was opened for settlement shortly after the war. For a time the Oatka was called Allan's Creek after the area's first settler, Ebenezer "Indian" Allan. Its waterpower facilitated early 19th-century European settlement of the abundant fertile lands in the Holland Purchase. Today it remains an important regional resource, used for water supply and recreational purposes, and actively protected to assure water quality. It is a popular trout stream, stocked from the oldest fish hatchery in the Western Hemisphere near its mouth. A dam in Le Roy makes the section below it a losing stream, dry during the warm months of the year as the stream flows through subterranean channels. Course Several small streams, some of which ultimately rise to the north at elevations of almost , come together to create the main stem of the creek amid the fields and woodlots on the high plateau in Gainesville just south of the Warsaw town line, a short distance west of Silver Spring Road. The new stream flows first south a mile, then turns northwest paralleling the Norfolk Southern railroad tracks toward the small hamlet of Rock Glen. There it crosses for the first time New York State Route 19 (NY 19), which it will parallel closely for much of the rest of its length. To the west of Rock Glen, it passes through the narrow gorge that gave it its name, emerging at another hamlet, Newburg,