You can't ride along the shore at high tide and we had no boats on our last expedition.
7 seconds sound clip from the Planet of the Apes (1968) movie soundboard.
You can hear this line at 01:28:30 in the Blu-ray version of the movie.
Quote context
[...]
- Where does this river lead to?
- It flows into a sea some miles from here.
- That's where we'll find the diggings.
- You can't ride along the shore at high tide and we had no boats on our last expedition.
- You never told me, why do you call this a Forbidden Zone?
- No one knows. It's an ancient taboo set forth in the Sacred Scrolls.
- The Lawgiver pronounced this whole area deadly.
[...]