One good exercise when pregnant is swimming. It is considered the safest exercise for it poses a very low risk of injury. Swimming is a low-impact exercise that uses the large muscle groups in the arms and legs. Despite being low-impact, it provides a lot of benefits. It provides good cardiovascular benefits, improves circulation, increases muscle tone and strength, and helps build endurance, which are good for you and your growing baby.
So get on your feet and put on those Maternity Swimwear and hit the swimming pool. Just take it easy and don't overdo it though. And consult your physician or midwife before you go swimming, especially if you haven't been swimming before your pregnancy.