Can I patch a vinyl liner leak underwater without draining the pool?

Yes, you can fix a small vinyl liner leak without draining the pool. Use an underwater vinyl liner patch kit with special glue that cures submerged. Clean the area, cut a patch overlapping the hole by at least an inch, apply glue to both surfaces, press for 30 seconds, and let cure 24 hours before running the pump. It works for punctures up to dime size, but for larger or seam leaks, drain and weld instead.