What Causes Algal Blooms in Waterways
Launch library · evergreen read
Algal blooms are rapid, dense growths of algae that occur when conditions align in a waterway: warm temperatures, still water and, most importantly, an oversupply of nutrients such as nitrogen and phosphorus. These nutrients commonly enter waterways from fertiliser runoff, sewage overflow or eroding soil.
Once a bloom takes hold, it can block sunlight from reaching plants beneath the surface and, as the algae eventually die and decompose, consume large amounts of dissolved oxygen in the process. That oxygen depletion is often what causes fish deaths associated with severe blooms, rather than the algae itself.
Some bloom forming species also produce toxins harmful to animals and people, which is why waterways are sometimes closed to swimming or fishing during an active bloom. Managing the nutrient inputs that trigger blooms in the first place is generally more effective than trying to treat a bloom once it has started. Reducing fertiliser runoff, maintaining vegetation along waterways and properly managing sewage overflow all address the same underlying nutrient problem from different directions.