An artificial lake created over a hundred years ago now, with it's own ecosystem that has developed around it.

And rivers still flow from that downstream, likely entering the water table of a much larger area than the lake itself. Despite it being "artificial", the water still passes through it to downstream ecosystems, as it did before any dam construction. While they may be lower volume due to the drought and limited releases from the lake, replacing that with "Salt water or nothing" would still be a massive change.

An artificial lake created in part by damming a river system.

If you don't think that would have much impact, start advocating to alleviate western US water concerns by pumping from the Great Lakes and reversing the course of the St Lawrence River to flow from the Atlantic into the lakes. I'm sure people will be very receptive.

It's an artificial lake that provides much of Panama's fresh drinking water, apart from supporting the locks.