I have disc bulge at l4-l5 and a small gap in sacrum, with radiating pain in right leg, I wanted to know, whether swimming is good for my condition

Excellent, but. Swimming if done properly helps ameliorate back pain. It is a low impact aerobic workout that is easy on the back and spine. Swimming should be performed under close supervision of the professionals who understand the limitations and special needs of back pain, and can address individual health needs.