I have water in backseat floorboard. Am unsure why or how to fix it. on 2001 Chevrolet Camaro

The backseat has water after rain or washing. How can I repair it and why does it happen? I have read about clogged drains but I have no idea where the drains are located or how to clear them or if this is the problem. Thank you

Asked by for the 2001 Chevrolet Camaro
check seals around windows or bad weather stripping around trunk or doors