Researcher Liz Denman, now a member of the Landscape and Urban Design group at VicRoads, explains that high levels of nitrogen and phosphorus can quickly go from nutrient to contaminate. The levels stimulate algal "blooms" -- or higher than normal algae content in water bodies. Algae consume oxygen in the water, especially as they die and decompose. They also block the sun from reaching areas below them, upsetting the natural state of the water body. The lower oxygen levels can result in fish deaths, a loss of biodiversity in the waters, and dead zones