Something in the Water

Salmon are transporting pollutants to streams, and the harmful chemicals are being taken up by other fish, researchers have discovered. Some of these stream-dwelling fish, such as trout, may need monitoring to ensure they don’t threaten the health of people who eat them.

It’s well-known that migrating animals can carry pollutants from one area to another. Pacific salmon, for example, eat prey containing persistent organic pollutants (POPs) in the ocean. When the salmon swim to streams to spawn, they bring their chemical baggage with them.

A team of researchers wondered if other fish in the streams were picking up these contaminants from salmon. They collected brook trout, white suckers, and other fish from tributaries of the Great Lakes, where salmon spawn each year. Some fish came from parts of the stream with salmon, while others were sampled from areas cut off from the spawning.

Fish that shared the stream with salmon had much higher POP levels than those in salmon-free areas, the authors report in Environmental Science & Technology. In the Lake Michigan tributaries, pollutant concentrations were 8 to 29 times higher in the fish from salmon-spawning segments; in Lake Huron tributaries, the pollutant levels were 6 to 12 times higher.

If managers remove dams that currently separate parts of the stream from salmon spawning, even more fish could be exposed to the contaminants. Bald eagles also feast on salmon in those tributaries, the team notes.

The findings could be worrisome news for people who eat the fish in these streams. Managers may need to keep a close eye on pollutant levels “to alert consumers of potential health risks associated with consuming trout from streams receiving salmon runs,” the authors say. Roberta Kwok | 25 July 2012

Source: Janetski, D.J. et al. 2012. Resident fishes display elevated organic pollutants in salmon spawning streams of the Great Lakes. doi: 10.1021/es301864k.

Image © photographer3431 |



  • tom July 25, 2012 at 8:18 am

    The entire world is so polluted and poisoned by zillions of chemicals unknown in nature that one despairs that any venue remains free of them. Hopefully our rogue species will kill itself off before the entire web of life succumbs to our idiocy.


  • Kelly July 25, 2012 at 8:22 am

    Removing dams are far more important to the ecosystem as a whole than worrying about cross contamination of contaminants. Plus, we should focus on the source of chemical pollutants rather than blaming the fish.


    • tom July 25, 2012 at 6:20 pm

      While I share your hatred of dams, I am afraid that they are rather trivial when we speak of poisoning the entire biosphere with thousands of exotic chemicals, largely untested, the effect of which is unknown either singly or in combination. Such usage could have the eventual effect of killing all life on earth. No one is “blaming the fish”!


  • D July 29, 2012 at 6:42 am

    Dam removal can have positive ecosystem effects and is often worth considering, but will usually involve trade-offs under any circumstances. Please be aware that the salmon in question have been stocked by state agencies for sport fishing and removing obstacles to their passage would not restore a native population, as in Pacific and Atlantic basins.


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