Golden Brown Algae (GBA) More nutrients, like phosphorus and nitrogen are entering the lake causing plants like this algae to grow. Nutrients from surface runoff typically cause algae floating on the water surface or in the water column to grow. When these microscopic algae die, they sink to the bottom and decompose.

The appearance of "brown algae" in lakes is typically caused by diatoms, which are a specific type of single-celled algae characterized by their silica-based cell walls. Several environmental factors contribute to their growth, primarily an abundance of nutrients like phosphorus and nitrogen—often resulting from agricultural runoff, lawn fertilizers, or leaky septic systems. Silicates, which are minerals naturally present in rocks and soil, are also essential for diatoms to build their glassy shells. High silica levels combined with cool water temperatures and low light conditions—common in early spring or late autumn—allow these organisms to outcompete other types of algae. Another factor can be "lake turnover," where the shifting of water layers brings nutrient-rich sediment from the bottom to the surface. While diatoms are a vital part of the aquatic food web, excessive blooms can create an unsightly brown film on rocks and docks. In 2026, lake management teams often use "phosphorus binders" or promote vegetative "buffer zones" along the shoreline to filter out the nutrients that trigger these blooms, helping to maintain the ecological balance and aesthetic clarity of the water.