Legally, you do not have to be certified to scuba dive. However, most dive shops will not take you out for dives or rent equipment to you without a Scuba Certification Card.
However, there are a number of options for those who do not wish to obtain a Scuba Certification and who will only be diving on occasion.
There are many organizations that offer “introductory” scuba courses. You will not receive a scuba certification from these courses, but you will be able to dive under the supervision of an instructor after passing a basic diving skills test and learning some basic diving safety. The availability of these programs vary from organization to organization.
In any case, it is always a safe bet to take a scuba diving course to get yourself acquainted with diving, to maintain your personal safety, and to see if getting your Scuba Certification is something you wish to pursue.