Video captured on stock PS5.
When you play through the normal game narrative and complete the "I'm Good With That" mission where you defeat Carlos, you can subsequently return to the ripper complex, but at that point, many areas are blocked off. You cannot explore the full dam and view the reservoir in its original pre-flood form. You cannot explore the area beyond the dam. You cannot explore the ripper lodge or the buildings near the ripper lodge.
However, if you can manage to sneak into ripper territory early in the game, you can casually wander around all of these areas in their original form. This video provides a full tour of all of these areas before the dam has been destroyed.