The 2005 discovery of what was then thought to be feminized fish caused by sewage outfall off the Southern California coast were actually not intersexed, but rather were the cause of accidentally contaminated tissue samples. The story, which was widely published, initially had blamed the intersexed fish on sewage outfalls that empty treated sewage between 2 and 5 miles off the coast of Los Angeles and Orange counties.
Intersexing occurs when male fish are exposed to hormone-like pollutants. This causes males to have testes that act like ovaries and grow eggs. The so-called findings caused so much concern that the local sewage agencies funded a $750,000 follow-up study of 600 more fish in 2006, and failed to find a single intersexed fish.
When scientists from the Southern California Coastal Water Research Project went back to the same locations where the initial test subjects were captured, they were unable to find any half male/half female hornyhead turbot (Pleuronichthys verticalis) and sole, flatfish that reside on the sand bottoms that are common off Southern California. So the scientists retested the original fish samples, reread the pathology report and determined that the eggs found on the males were not located inside their testes. They labeled the eggs as stray eggs that had apparently dropped on the fish tissue of the male fish.
While the notion of these specific intersexed fish proved to be false, the scientists did note in a recently published, peer-reviewed paper that sewage outfall has had an effect on estrogen levels of the hornyhead turbot. When captured near the sewage outfalls, the estrogen levels of both the female and male turbots were measured at half the levels of those captured in sites that are not contaminated by sewage outfall. They attribute this to anti-estrogenic chemicals near the sewage outfalls, but also noted that the population levels of the hornyhead turbot seem to be healthy.