If you're not a native, you may mispronounce "Olentangy". Don't be embarrassed - it's how we tell the natives from the outsiders.
Most have problems with the "tangy" part. It's NOT pronounced like the NASA orange drink + the OSU President's name, as in "tang-gee".
Rather it's pronounced like something that's hard to get in Ohio - a "tan". And when someone does get a "tan", we might say "GEE" you have a "tan". So it's "tan-gee" with emphasis on the "tan".
Now you can sound just like one of us.