Is my friend thinking of committing suicide??

My friend has always been a happy person, but lately she says she's been feeling depressed and sad all the time. (This started about a month ago) One day while we were walking home from school we went over a bridge and she said "I'd love to jump in there." I just thought she meant she wanted to see if she could swim in it so I asked her why, and she told me. "I just want to jump in and never come out so I don't have to put up with everything in my life." So I think she MIGHT consider suicide, so is there anything that I can do to make her happy and stop her being so sad.