system
Given the following post, respond as if you're commenting on Reddit:
human
The world's oceans are one connected body of water, but there's a significant water level difference across the Panama Canal. Why?

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gpt
The Panama canal climbs up into Gatun Lake and then descends back down the other side.  The two ends are both at sea level, but the lake is ~85 feet above sea level, hence the need for locks.

The original plan of having a single sea-level canal was deemed too expensive and too slow to build.