The seasonal changes in the phosphorus content of the bay’s waters are similar to the seasonal changes of their nitrogen content, although nowadays the nutrient load from the river water is predominantly nitrogen-based. Furthermore, the phosphorus carried in the river water is often bound to solids and other compounds, making it difficult for algae to utilise. The total phosphorus levels of the waters are approximately 1.5 times as high as in other bay areas throughout the year.
The long-term development of the bay’s phosphorus content has largely followed the development of the bay’s nitrogen content, though the removal of phosphorus in the wastewater treatment process was increased considerably in the late 1970s. This can be seen in the accompanying graph as a decrease in total phosphorus. Over the years the phosphorus content of the bay’s waters has decreased to approximately one fifth from the mid-1970s, when the phosphorus load was at its highest.