As of February 1, 2008, the U.S. Board on Geographic Names had identified 5,564 natural streams in the State of Colorado.  Of this number, 147 larger streams (2.6%) were named river and 11 (0.2%) were named rio.  The vast majority of the Colorado streams (5082 or 91.3%) were named stream.  Of the remaining Colorado streams, 122 (2.2%) were named arroyo (creek), 60 (1.1%) were named wash (creek), 44 (0.8%) were named stream, 18 (0.3%) were named stream, 17 (0.3%) were named stream, 17 (0.3%) were named stream, 15 (0.3%) were named stream, 10 (0.2%) were named River delta, but not a single stream was named stream.  Perhaps the strangest stream name in Colorado belongs to the West Fork East Fork Williams Fork located in Garfield County, Colorado.
Question: Which name was the least common for natural streams in Colorado?
Answer: River delta