Swimming While Pregnant?

My fiancé and I recently relocated and since it's getting warmer, I'd like to start swimming. My original plan was to swim every day until I found out I was pregnant. However, I'd still like to stay active while pregnant, so is swimming safe? I wouldn't be doing any hard swimming, just across the lake and back maybe a couple times a week. I also do yoga, so I'll be doing that on top of swimming. What are your thoughts? What do you do to stay active while pregnant?