A surprising finding from the waters of Seattle's Puget Sound reveals that the opioid epidemic devastating human communities in the U.S. could be harming marine life as well.

Every two years, the Washington Department of Fish and Wildlife (WDFW) transplants bay mussels raised in clean waters in Whidbey Island, WA to locations around Puget Sound in order to monitor pollution levels in the water. Since mussels are filter feeders, area scientists can get a good idea of what contaminants are present in the environment by examining which have built up in the mussels' tissue after two to three months of exposure.

This year, for the first time, one of those contaminants was oxycodone.

"It's telling me there's a lot of people taking oxycodone in the Puget Sound area. The contamination is likely coming from wastewater treatment plants," WDFW biologist Jennifer Lanksbury told local news outlet KIRO7 on May 23.

King County Wastewater Management told KIRO7 that they cannot filter out drugs specifically, which end up in urine that is then flushed down the toilet.

The oxycodone-contaminated mussels were found in mussels from three of the 18 areas tested, one in Seattle's Elliott Bay and two near the shipyard of Bremerton Island.

The findings were announced by the University of Washington's Puget Sound Institute (PSI), which helped with the study, conducted May 9 and widely reported last week.

PSI researcher Andy James explained in the University of Washington release that the mussels did not pose a risk to human consumers, since they were found in very urban areas far from where commercial mussels are gathered.

"You wouldn't want to collect (and eat) mussels from these urban bays," James said.

The release further explained that the dosages found in the mussels were thousands of times smaller than the amount that would impact a human and likely had no impact on the mussels either.

However, oxycodone levels in the Puget Sound area could pose a risk to fish. Studies have found that zebrafish will get high off of opioids, and scientists are worried that salmon and other Puget Sound fish could react similarly, according to the release.

The mussels also tested positively for other drugs like antidepressants and antibiotics.

"Those are definitely chemicals that are out there in the nearshore waters and they may be having an impact on the fish and shellfish that live there," Lanksbury told KIRO7.

Of particular concern, according to the University of Washington release, is the chemotherapy drug Melphalan, which interacts with DNA in ways that might cause cancer. It was found in mussels in levels relative by weight to the recommended human dose, "levels where we might want to look at biological impacts," James said.

Lanksbury told CNN the results were made possible by extra funding, which WDFW used to test for "contaminants of emerging concern" such as prescription drugs and personal care products. Previous studies had focused on pollutants like PCBs, pesticides and toxic metals.

Other important "contaminants of emerging concern" found in the mussels were four types of surfactants from detergents and cleaning products that can have an "estrogenic effect" on organisms like fish, "feminizing male fish and making female fish reproductive before they're ready," Lanksbury told CNN.

After these results, the WDFW will seek additional funding to continue monitoring prescription drug levels in the water, KIRO7 reported.

"People should be wary," Lanksbury told KIRO7. "Hopefully our data shows what's out there and can get the process started for cleaning up our waters."