Agreed, where I lived in NY as a kid we had the Schuylkill River and it was pronounced more like "School-Kill" or "Skoo-Kill" as surgent suggests. I would be curious where you heard it as "Sish-yoi-le-kill".
Admittedly I have heard a lot of other words pronounced differently in local areas, for example "Louisville" in Colorado is "Lewis-ville" not "Louie-Ville" as it is in KY, and Cairo in Illinois is pronounced "Kay-Row" (like the boys name Ray).
Hey guys, I heard it pronounced "Shish-yoi-le-kill" from one of my buddys that lives in Gunnison. He said he climbed it 3 years ago and someone at the coffee store in town said it was pronounced like that so thats where I got it from. It could be pronounced either way, I have no clue.