That yellow stuff that washes ashore in May and June is primarily tree pollen, specifically from coniferous trees like pines. These trees release large amounts of pollen during their pollination season, which is typically in the spring. The pollen is carried by wind and lands all over our watershed, including on the water, which eventually washes up on shores.
Tree pollen is non-toxic and is not harmful to the ecosystem — it is a natural occurrence and doesn’t pose a threat to aquatic life or water quality. While pollen can temporarily discolor the water and create a film on the surface, it will eventually sink to the bottom of the lake as it becomes waterlogged.