Pollutants in Lake Tahoe have worsened over the past decade

Nitrate and phosphorus feed algae, which reduce lake clarity. Nitrate comes mostly from the air, largely from vehicle exhaust. Phosphorus, found in soil, washes into the lake from forests and urban areas. Fine particles flow into the lake through stormwater. These contaminants spike in some years because of heavy urban runoff during storms but they have worsened in recent decades.