This weekend, our lakes will boil with the splashing masses, as we head to the water to cool off from the summer sun, catch thrills by watercraft and sustenance for our tables.

But the content of our waterbodies is a testament to how we treat them.

Michigan Department of Health and Human Services officials sent a reminder this week to local residents and visitors to avoid foam on Michigan lakes, rivers and streams.

Foam is a familiar sight on many of our waterways. Naturally occurring foam is usually off-white and/or brown, has an earthy or fishy scent and piles up in bays, eddies and dams, according to the department. But — ask the residents of Lake Margrethe — some foam is decidedly unnatural.

Foam can contain harmful chemicals or bacteria, and high levels of per- and polyfluoroalkyl substances (PFAS).

PFAS-containing foam is bright white in color, lightweight and may pile up along shores or blow onto beaches.

The health department recommends no contact with foam for humans and animals, or rinsing off quickly if exposed. They say some studies of people have found that repeated high exposure to PFAS has been linked to liver damage and thyroid disease, among other health effects.

At Camp Grayling, fire trucks filled with PFAS firefighting foam were topped off nightly from the 1970s until about 1986, as tanks leaked about 80 gallons each day, according to a federal report. Because the form was so corrosive, officials would perform nozzle checks on the tanks by discharging the foam directly into surface waters, the report said.

“Fire truck tanks were washed out into Lake Margrethe as regular practice during routine maintenance. The frequency and quantity of tank washout is not known. Since AFFF (Aqueous Film Forming Foam) was regularly used as ‘wet water’ in truck tanks during the 1970s and 1980s, PFAS may have been directly washed into the lake,” the report states.

We have since come to know the tragic legacy of PFAS, now dubbed “the forever chemical” — because it does not naturally degrade in the environment, and now can be found in varying amounts in water around the country.

Though Camp Grayling was Michigan’s first “official” PFAS site, these sites have sprung up across the country, from Charleston, N.C., to Stuart, Fla., from municipal water systems to private water wells. The Traverse City area has had several sites with PFAS concentration, including a neighborhood where a groundwater plume from a 1995 tire fire found its way into homes; and a plume from the airport found its way to faucets in the Pine Grove subdivision.

The makers of the chemical have been called to account, as we try to put our arms around a large-scale cleanup.

The legacy of PFAS will continue long after the memories of this holiday weekend fade. So, as we blow the foam off an icy beverage and head to the beach, remember that our waters continue to record our treatment of them.