Anyone who tells you you should not swim at the end of your third trimester, or should not work out in water, is absolute bollocks.
When you do exercises in water, your abdominal muscles are engaged and lengthened because they’re working to keep you balanced. And the buoyancy of the water actually makes it easier for your to carry your weight, in whatever exercise position you are trying to execute.
Also, in water, you weigh just a tenth of what you do on land. Which means bobbing weightlessly, feeling both lighter and more limber. As you enter 3rd trimester, this should be a real treat!
Exercising in water is ideal for expectant moms as the cool water and soothing aqua environment enables you to comfortably perform more repetitions than you could on land. That means you can challenge yourself, but the support the water provides makes it safer to do those extra reps. Then again the pressure from the water also adds resistance which makes your muscles work harder to push against it, which is great for muscle toning. Pressure from water can also help relieve swelling in your extremities.
Intermediate and advanced swimmers can go for the 2,000-yard swim (i.e., 80 laps in a 25-yard pool.) You can try this workout using your favorite stroke or alternating between different ones:
5 sets of 100 yards (4 laps) at a moderate-pace, with 10 to 20 seconds rest between each set. Rest and stretch for one minute when you’re done.
6 sets of 50 yards (2 laps), focusing on your form. Rest 20 to 30 seconds between sets. Rest for 1 minute when you’re done.
10 sets of 100 yards (4 laps), focusing on speed with effort that’s about an eight on a scale of one to 10. Rest 10 to 30 seconds between sets. Rest for 1 minute when you’re done.
Grab a kickboard and do 4 laps, just kicking.
Ditch the kick board and swim four more laps at an easy pace to cool down.
And though you don’t feel like you are perspiring in water, you are. You are losing fluids. So make sure you drink tons of water. Lack of water/dehydration can cause uterine contractions.