There won't be. Scientific intuition and the available studies suggest that apart from perhaps in the immediate vicinity of where they pump the salt back in, the effect is minimal, no matter how much desalination you perform.

It's what you'd expect, in fact. The state of California (if my back of envelope calculations are correct) uses in total about 66 cubic kilometres of water each year.

If you produced California's entire water supply by desalination, this would be akin to removing 1/10,000,000 of the Pacific's water every year. It's a miniscule amount, and is of order of magnitude the same as not letting the Colorado reach the ocean.