Sampling for microplastics is challenging. Some microplastics float on the surface (and are blown to other locations), some remain suspended at depth (and might escape the dam), and some sink into the sediment (and stay there forever). To capture all types, we collected a variety of samples.

• Surface water samples collect microplastics floating on the surface.

• Water column samples collect microplastics suspended at varying depths.

• Sediment samples collect microplastics that have sunk.

• Rainwater collects microplastics suspended in the air.

• Beach tests find microplastics that have floated in and been blown onto the shore.

The reality of science is that time and money are always limited, so we performed as many tests as we could and then extrapolated.