**Depressed Fish? How Prozac in Lakes and Rivers Could Harm Aquatic Life**

An Australian study has detected traces of the antidepressant fluoxetine in fish from freshwater lakes and rivers.

An Australian-Italian joint study has detected traces of the antidepressant fluoxetine—commonly known as Prozac—in lakes and rivers, potentially impacting freshwater fish.

The five-year study, conducted by scientists from Monash University’s School of Biological Sciences and the University of Tuscia’s Department of Ecological and Biological Sciences, investigated the effects of pharmaceutical residues on fish in Australian freshwater environments.

**Why Are Antidepressants Found in Lakes and Rivers?**

Fluoxetine, the third-most popular antidepressant and the first commercially successful selective serotonin reuptake inhibitor (SSRI), is one of the main drugs detected in freshwater systems.

When patients take prescription medications, their bodies do not absorb all of the drug. Residual medication is excreted in urine or feces, which then enters waterways through toilets and waste treatment centers. This residue can persist in the water, where aquatic life absorbs these leftover pollutants.

Fluoxetine has a "bioavailability" of about 70 to 72 percent, meaning this portion enters the bloodstream, while the remaining 28 to 30 percent is excreted. Many modern wastewater treatment plants are not equipped to filter out pharmaceutical chemicals effectively. Consequently, treated water reintroduced into waterways may still contain pharmaceutical contaminants that can be absorbed by fish.

Additionally, unused or expired medications are often improperly disposed of via toilets, exacerbating the issue.

**What Did the Study Find?**

In 2016, researchers collected 3,600 male guppies (Poecilia reticulata) from Alligator Creek in North Queensland to investigate fluoxetine contamination. The study found no evidence of contamination in the fish.