That said, I can't quite understand the complaint. It's either take the freshwater out of the lake and into the ocean or take the ocean water into the lake (or invest build the entire length without using natural bodies). The former seems to make a lot more sense and is effectively what's supposed to happen with water eventually anyways.
Imagine one lock is currently filled to the high level, while the other is currently filled to the low level. The locks have been closed. As you let water from the high lock flow into the low lock through Archimedes screws, those screws can lift a weight, until they have equilibrated at the midpoint of the high and low water levels. But you have raised the weight and can now use that to power the draining of the lock that has only halfway sunk in level, by pumping its water to the lock that has only halfway risen. Apart from friction there is no energy consumption. Slow quasistatic transfer drives the friction energy consumption to 0. In practice you want to use an "extra" weight to attain higher pump speeds, and then recover the kinetic energy. That will consume more friction energy, but a small number of solar panels suffice, the energy is not used to lift water, but to overcome friction (haste makes waste).
Prior to the rivers being damned to make the lakes, they just emptied into the ocean directly. No net new fresh water is being created, we're just holding it up for a bit so we didn't have to build as much canal.
If anything, we're diverting more of that aater away from the Atlantic and towards the pacific than would normally have drained in that direction by doing this.
A) the BBC retardedly misreports how the Panama Canal is operated today, or if
B) they correctly report how the Panama Canal is operated retardedly
which is why I phrased it that way...
I am only interested in the physics, not the politics...
but I wouldn't protest if you clarify an issue you seem or pretend to care a lot about...