Microplastics found in Glacier National Park's Lake McDonald

Lake McDonald in Glacier National Park is one of the most pristine lakes in the world. If one is in a boat and looks down into its waters, you can see the bottom, even 40-50 feet down.

But a study this summer found potential trouble in the lake — microplastics. Microplastics are tiny bits of plastic that are less than 5 mm in size, or 0.2 inch.

This summer, through funding from the Glacier National Park Conservancy, fisheries technician Brandon Barnes and Chris Downs, the aquatic and physical science program manager for Glacier, sampled a relatively small portion of the lake using a simple net typically used to sample water for plankton.

They overlayed a 1 kilometer grid over the lake using Google Earth and using a random number generator, they selected approximately 10 sites to sample each day down to a depth of about 20 meters, sampling just 1.41 square meters of the lake at a time.

From there, most of the water was decanted off and the remaining samples were poured into 45 milliliter vials.

The samples were taken back to the lab, filtered through a coffee filter and then allowed to dry. They then used a 10 power dissecting scope to go through the samples and identify possible microplastics.

Sampling was low tech. Pieces that looked like plastic were subjected to the “hot pin” test. Plastic curls up when subjected to heat.

If the hot pin melted the sample, it was considered plastic.

All told, they conducted 41 vertical hauls on the lake and sampled a very small portion of the water — about 57.8 square meters.

To put that in perspective, the total water volume of the lake is estimated to be about 1.537 billion square meters.

“We barely scratched the surface,” Downs noted.

Still, they found plastics. A total of 11 suspected microplastics were found in nine different sites along the lake.

Most were very small pieces of black or red fibrous materials, along with what appeared to be small fragments of fishing line.

The findings show just how pervasive plastics are in the environment, even in a pristine lake in a national park, Downs said. Plastics are in almost everything Americans use, from clothes to shoes to grocery bags.

The big question is what impact the plastic is having on the food chain.

The bits and pieces can be ingested by aquatic insects and other invertebrates and work their way up the food chain into birds and mammals.

The impact is unknown at this point.

Another problem in the lake is increased levels of nitrogen. Downs said that could be from recent wildfires, but it could also be from humans as well.

Nitrogen levels increase the nutrient level in a lake and cause more algae growth, reducing the lake’s renowned clarity.

Downs said more research is needed. They would like to broaden studies and examine other lakes for plastics as well.

Glacier is not alone. Yellowstone National Park has also found microplastics in some of its lakes and the plastic has been documented inside the stomachs of aquatic insects.

“It remains a high priority to see what’s going on,” Downs said.