Warming water temps, lower oxygen levels, etc., in the harbour are symptoms of a much larger issue.
After hundreds of years, we've created an environment that's becoming more suited to the Goldfish( and carp )than to some of our native species. We're spending millions of dollars trying to eradicate 'non-native' species from habits they are now adaptable too, while the will and means to restore the habitat to its original form doesn't exist.
In many ways, I think the genie is out of the bottle and we got what we got.