After the estrogen was introduced, the number of fathead minnows in the lake declined rapidly. Says Kidd, "The crash in the population was very evident and very dramatic and very rapid and related directly to the estrogen addition."
Meanwhile, the number of insects around the ecosystem increased, presumably due to lack of predation from the minnows. According to the study, the decline in minnows directly affected the fish who were higher up on the food chain. The team writes that the "biomass of top predator lake trout declined by 23–42% during and after EE2 additions, most probably an indirect effect from the loss of its prey species, the fathead minnow and slimy sculpin."
Once the estrogen was removed from the ecosystem, the number of fathead minnows surged once more to the pre-study population size.
Kidd told CTV News that feminized male fish have been observed in Saskatchewan's Wascana Creek, Ontario's Grand River, and Alberta's South Saskatchewan River. These attributes are likely due to sewage being released into the waterways. "It's a problem that we can certainly resolve with better waste water treatment," she says.