If so, rake away debris every year.
There is a major source of microplastics in your area - you consistently find flecks of polystyrene foam. Most are thumb-sized or smaller, trapped in pine needles on the west-facing shorelines. They are bright blue in the spring; by July they have faded, and by September they have disintegrated into microplastics. They are shredded by winter ice damage, not summer storms. This happens every year. In spring 2025, patches of foam flecks were observed as each of the orange squares was passed (see photo). To put the diagram in context, there would be only a few more squares in the rest of the lake, mostly in MacDonald Bay.
The student sampled the beach on one of those orange squares and found many macroplastics (> 5 mm) but no microplastics (< 5 mm). Over time, why did the macroplastics not degrade into smaller bits? Because this beach was private property and the cottager raked away the debris every year. If your beach regularly receives foam flecks, removing that material every year can help reduce the amount of plastic that can break down into microplastics. Regular cleanup cannot guarantee the absence of microplastics, but it is a practical way to reduce contamination.