The changes that can be observed include;
Cyanobacteria prefer alkaline environments and during active growth, the pH will be observed increasing. Excessive growth can result in much higher pH readings than observed in waters not affected by cyanobacteria blooms.
Dissolved Oxygen (DO)
Cyanobacteria photosynthesise during the day and respire at night. Water can become oversaturated with oxygen during the day. However, once respiration begins, the oxygen in the water column is quickly consumed. Too much or too little oxygen in itself can cause problems for other aquatic life. It is this switch in metabolism that is responsible for fish kills, often associated with blooms, and not necessarily the presence of toxins. Degradation and the sudden collapse of a bloom will also cause a rapid reduction of oxygen in water too. It is important to note, any bloom of algae, and not just cyanobacteria can cause oxygen depletion in the water this way.
Turbidity is the measurement of light scattering in water, by both organic and inorganic particles. Cyanobacteria and phytoplankton can vary in size and can contribute significantly to the turbidity of the water, particularly during a bloom.
Some cyanobacteria are buoyant and aggregate into thick scums on the surface of the water and along shorelines. The heat produced by the cellular metabolism within a scum can noticeably increase the water temperature around it.