Paced or Interval

I absolutely LOVE swimming, actually I am addicted to swimming. My mom used to be afraid I was going to sprout gills when I was younger. Over the last 3 months I have been in the pool getting back in shape. I have lost quite a bit of weight, which was only part of my over all goal. That being to loose weight, but get into an exercise routine I would stick with so I could keep fit. Right now I am swimming distance at a steady pace. That right now gives me an hour workout and it has kept me loosing around 2-3 lbs a week, which is perfect. My question is this....should I keep the pace/distance workout or should I go to some interval training workout? I was under the belief that workouts that went anaerobic caused your body to not burn fat, which is what I am trying to do for the time being. Would doing interval training, even though it is at faster rate accomplish what I am trying to do by increasing my heart rate to a greater rate over a longer period or would it be going against what I am trying to do?