I believe that in the United States (as opposed to Canada), the block dive depth must be six feet or more. A 50-meter pool in Long Beach, California, originally built for Olympic trials in the 70s, can no longer be used for long-course races because it is only 3 feet deep at one end. Instead, races are only short course (25 yards) held in the deep end (a 17-foot dive well). All of the pools where I have seen competition swimming have been six feet deep or deeper.
Thanks, Finny.