By the very same mental midgets, I present "hypomesus nipponensis". An important food fish native to the lakes and estuaries of Hokkaido, Japan, it was introduced to the San Francisco Delta of the United States. 70's.
Besides direct competition for nutritional resources and the possibility that wakasagi may prey on the eggs and larvae of Delta smelt, hybridization could either dilute the species or cause population decline due to sterilizing effects.
The answer for idiocy? Shut off the water to a vibrant bread basket of the United States.
So much for the "threatened" delta smelt. It's just another example of political fraud and was used to create a man-made "dust bowl" to accompany the upcoming economic meltdown. See "Great Depression".