Knowing how to swim is definitely a bonus, but does not limit you from trying and experiencing scuba diving.
You do not need to be a strong swimmer to enroll in the Discover Scuba Diving (DSD) program. You do, however, need to be comfortable in the water. The DSD program is aimed at introducing scuba diving to beginners. You will have a PADI Instructor with you throughout the dive who will supervise and ensure your safety.
For PADI Dive Courses, such as the PADI Open Water Diver course, you will need to be able to complete at least a 300 meter swim with a mask and snorkel in order to earn the certification. More advanced courses may have additional swimming requirements .