The city of Boulder is teaming up with two local agencies to help keep pharmaceuticals out of the water supply.

Saturday, the city, Partners for A Clean Environment and Boulder Community Foothills Hospital are hosting the first "Pharmaceutical Drop Off Day" and encouraging residents to bring their expired, excess and unwanted medications to the hospital, 4747 Arapahoe Ave., for proper disposal.

The event runs from 8 a.m. to 2 p.m. Both prescription and over-the-counter medications will be accepted, including pills, liquids, patches or inhalers.

The aim is to keep medications from being flushed down the toilet. Because Boulder's wastewater treatment plant has trouble removing all chemicals found in the medications, they find their way into local rivers and streams and negatively affect fish and other wildlife.

"We are working the event this Saturday with city of Boulder wastewater treatment personnel," said Bill Hayes, team lead for the PACEprogram.

Hayes said the city has a vested interest in the issue because if the problem continues, Boulder could be forced to update its wastewater treatment plant to remove the chemicals, which could be very expensive.

In 2003, small concentrations of prescription drugs, such as Tylenol and nicotine, were found in Boulder Creek water samples below the wastewater treatment plant. Studies in 2004 and 2006 discovered that fish just below the plant were changing sex; birth-control and epilepsy medication were cited as the cause.

"This has been an ongoing issue for quite a while," Hayes said. "Now these chemicals are showing up in our drinking water."

Hayes said controlled substances -- prescription narcotics and pain relievers -- will be collected by Boulder Police, while non-controlled substances -- over-the-counter drugs -- will be disposed of through standard hazardous waste collectors and incinerated.

While it is only a one day event, Hayes said he hopes to raise awareness on the environmental problems medications disposed of improperly can have on local water and wildlife.

"This is an opportunity to educate the public," he said, conceding, however, it may not be enough to solve the problem.

"We need a year-round solution, for a long-term sustainability."