For those of you new to the Sierra, please read the following thread on how to cross creeks/rivers safely, and those of you who are experienced, please take your time re-reading this thread to brush up on some of the techniques and dangers involved with crossings. Don't become a statistic!
Here is a video from Yosemite NPS about the dangers of creek crossings:
Rivers and creeks are running high, and they are beautiful... but deadly. Please be sure to keep back from swiftly flowing water. Be aware that wet rock can be surprisingly slick. Most people who end up rescued or recovered from the river didn't intend to go in.