Estrogen from birth control pills that passes through sewage treatment systems can have disastrous effects on fish populations, according to a Saint John biologist.

Karen Kidd, a biologist at the University of New Brunswick's Saint John campus, spoke at the American Association for the Advancement of Science's annual conference in Boston on the weekend.

Kidd's research has found that when estrogen from birth control pills passes into lakes and streams it can kill some wild fish populations.

She said her study, which has been published, has led her to believe that more needs to be done to regulate chemicals that enter the environment.

"It's the first study to show that it doesn't take a lot of estrogen to cause a collapse in a fish population," she told CBC News.

Kidd's team conducted seven years of research at a designated research lake in northwest Ontario that was unpolluted and free of human activities and fishing.

After building an ecological snapshot of the fish and invertebrates in the lake, Kidd's research team introduced small amounts of synthetic estrogen into the water between 2001 and 2003 — levels that were meant to reflect the amount of estrogen introduced into water systems from treated municipal sewage.

Impact was wide

It was found that the estrogen had almost no effect on bacteria, algae and invertebrates living in the waters but had a dramatic effect on some species of fish.

Male fish began to feminize, producing egg proteins while the female fish produced more estrogen than normal, which slows sexual maturation and egg production.

Fathead minnows stopped producing and 90 per cent of its population was lost. Pearl dace in the lake also declined by about 86 per cent and trout by 30 per cent.

After three years of research the scientists stopped adding estrogen to the lake and the fish populations recovered.

Estrogen's impact on smaller fish can also have an impact on larger species that are dependent on them for food, Kidd said.

Kidd said she doesn't believe that women should stop using birth control pills but that more needs to be done ensure that estrogen is being removed from the wastewater. Kidd said the technology to remove estrogen from wastewater is available and can help existing treatment systems.

"Once we treat our wastewater … we can remove up to 95 per cent, sometimes 100 per cent of these estrogens," she said.

Governments should be looking more closely at water quality guidelines, she said.