Photo of foam from 2013 that possibly contains PFAS, near Barton Dam, Ann Arbor, by Rebecca Foster.
Photo of foam from 2013 that possibly contains PFAS, near Barton Dam, Ann Arbor, by Rebecca Foster.

The State of Michigan has released advisories to avoid exposure to river foam, which tends to form near dams. If you fish or recreate near dams, please review the information we have provided on ways to protect yourself from exposure to PFAS foam in a previous post on our Huron River Water Trail site here.

PFAS stay near the surface of the water. They are surfactants, made to create smooth, tightly bound, water-resistant, resilient surfaces. That’s why they were used for chrome plating of automotive parts, teflon coating for pots and pans, even the slippery covering on some brands of dental floss.


Dams churn river water into foam and areas below dams tend to trap foam. PFAS chemicals tend to concentrate in foam, so it’s best not to linger or fish immediately downstream of dams. PFAS have also been found in foamy sea spray, in rain in the Great Lakes, and in remote parts of the Arctic, so we know it can be transported through the atmosphere. It’s possible people in the mist below dams could inhale PFAS attached to tiny droplets.

The total level of PFAS contamination throughout the Huron River is way below where it was in 2018, largely due to filtration installed at a pollution source. Throughout most of the Huron, the concentration of various regulated PFAS contaminants are within the levels allowed for drinking water, but dams create foam by churning water to a froth, because PFAS concentrates in foam,  that can lead to hot spots of PFAS contamination. PFAS concentrations in foam are often 100 to 10,000 times higher than in the surrounding non-foamy water. A natural, flowing stretch of the Huron River without dams may limit vigorously agitating the water to a froth and creating foam hot spots with potentially harmful concentrations. But again, little is known about how strong that affect would be.

Dams also impede the natural flushing process of a river, trapping contaminants behind them. PFAS tend to cling to natural and artificial structures. In natural river flow conditions, PFAS generally don’t sink into the bottom sediment as much as other contaminants do, but restricting the flow of the river may give it more time to linger in still water, get buried in sediment, cling to artificial structures like pipes and concrete, and build up in fish meat over time. A natural, flowing river removes these impediments and allows PFAS to flush as quickly as possible.

What we do know is that dams are bad for water quality overall, and that they pose inherent danger to anglers and paddlers that get too close. PFAS contamination adds another reason to be careful around dams.

More about PFAS More about Dams